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#1351294 - 04/01/02 04:38 PM Re: Feel free to ask Myles
peel_dup1 Offline
Senior Member

Registered: 03/05/02
Posts: 60
Loc: Toronto,,CANADA
Myles,

Sorry if this is repetitive, Im curious to know how much swapping a 12ax7 tube in my Rocktron Voodu valve rack preamp would affect tone? The voodu runs into a Mesa 50/50

Thanks Peel

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GP Island
#1351295 - 04/01/02 10:13 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5037
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by peel:
Myles,

Sorry if this is repetitive, Im curious to know how much swapping a 12ax7 tube in my Rocktron Voodu valve rack preamp would affect tone? The voodu runs into a Mesa 50/50

Thanks Peel
Peel,

Better quality tubes make any amp sound better.

The issue with rack mount components though, makes the differences a little harder to quantify. In most rack mount preamps, there is all sorts of other circuitry, and at times for the EQ, a lot of solid state items in the mix. This is one of the reasons that rack systems fell out of favor somewhat, compared to the era back in the 80's .... people did not know how to match the preamp and the amp, or would use a nice preamp with a solid state amp, etc.

Its easy enough to try though, and pretty cheap too. You can buy a nice NOS RCA or Sylvania tube from folks like KCA or Tube World, for less than $25 in most cases. Thats nearly as cheap as a retail "new" tube. Pop it in, and listen. If the note does not seem to have a lot more "life", then there are other factors that need to be addressed.

Hope this helped at least a little....

Regards,

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#1351296 - 04/02/02 12:41 AM Re: Feel free to ask Myles
Lance-a-not Offline
Member

Registered: 03/03/02
Posts: 12
Loc: Woodstock,GA,UNITED STATES
Quote:
Originally posted by JamesPeters:
Hey Myles. I just finished my first "production" (non-prototype, professional looking) amp a few days ago. Just figured I'd stop by here to let you know you can check out pics on my site if you like. Later!
James,

Whoops, I was ill this weekend... I missed that there were clips. While I don't have Myles' expertice, my ears wanted me to let you know you got a real winner there, VERY, VERY NICE! I am thinking my univalve may be needing a friend.

Would the amp be able to run a KT66 ?

Lance

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#1351297 - 04/02/02 02:13 AM Re: Feel free to ask Myles
sgguitarzz Offline
Senior Member

Registered: 04/01/02
Posts: 91
Myles I hope you can help.
My Mark IIB has a 60/100 switch. I use it in the 60 watt position. According to the Boogie manual when used this way only the 2 outside tubes are being used. I believe the 2 inside tubes are kind of in standby. When in 100 watt mode all 4 6L6's are being used. Is this correct? I have just put some Yellowjackets in (2) so I put them in the two outside slots and left the 2 inside as they were (2 JJ 6L6GC's) but the THD guide says in a 4 power tube amp to put them inside when using 2 YJ.

Dennis

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#1351298 - 04/02/02 02:47 AM Re: Feel free to ask Myles
JamesPeters Offline
Senior Member

Registered: 03/07/02
Posts: 39
Loc: Calgary, Canada
Quote:
Originally posted by Lance-a-not:
James,

Whoops, I was ill this weekend... I missed that there were clips. While I don't have Myles' expertice, my ears wanted me to let you know you got a real winner there, VERY, VERY NICE! I am thinking my univalve may be needing a friend.

Would the amp be able to run a KT66 ?

Lance
Thanks Lance! KT66 you say...ok I just looked at some data sheets and I think it's a go. I'll have to actually get my hands on one to test, to make sure it doesn't draw too much current--but I honestly think it'll be fine. (Now, where can I get a KT66... \:\) )

I'll see if I can scrounge one somewhere in town. If you like, I can email you when I find out--it might be up to a week depending on if they're any KT66 tubes in stock or not.
_________________________
http://petersamps.com
Handmade tube guitar amps

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#1351299 - 04/02/02 04:03 AM Re: Feel free to ask Myles
JamesPeters Offline
Senior Member

Registered: 03/07/02
Posts: 39
Loc: Calgary, Canada
Oh hey I just realised--that's a honkin' tall tube! I may have to change the dimensions of the amp to allow it to fit. What's your KT66 measure--both seated depth (not including the pins, after the bottom of the base) and overall length?
_________________________
http://petersamps.com
Handmade tube guitar amps

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#1351300 - 04/02/02 08:53 AM Re: Feel free to ask Myles
fantasticsound Offline
10k Club

Registered: 04/07/01
Posts: 16867
Loc: Madison,TN, UNITED STATES
Hi Myles,

My question was missed, as well. I had difficulty getting internet access on the rest of our Middle East tour, so I had few chances to bump the thread. Here it is.

Neil\'s tube question regarding a Peavey Delta Blues 2 - 10" combo.

Thanks for any assistance you can provide.
_________________________
It's easiest to find me on Facebook. Neil Bergman

Soundclick
fntstcsnd

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#1351301 - 04/02/02 02:48 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5037
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by sgguitarzz:
Myles I hope you can help.
My Mark IIB has a 60/100 switch. I use it in the 60 watt position. According to the Boogie manual when used this way only the 2 outside tubes are being used. I believe the 2 inside tubes are kind of in standby. When in 100 watt mode all 4 6L6's are being used. Is this correct? I have just put some Yellowjackets in (2) so I put them in the two outside slots and left the 2 inside as they were (2 JJ 6L6GC's) but the THD guide says in a 4 power tube amp to put them inside when using 2 YJ.

Dennis
sgguitarzz ...

You are correct.

On the Mark IIB, when you flip the 60/100 watt switch to the 60 watt position, the -52 volts that is normally supplied in the 100 watt position to the center two tubes is shut off. This effectively shuts down these tubes, yet leaves them in the circuit, so the impedience in teh output section stays the same.

In a 100 watt older Marshall amp for example, that does not have a switch, if you want to cut the power in half, you actually have to remove two of the tubes, but also you need to remember to change your output impedience switch to compensate for the loss of two tubes. In the Mesa, you do not have to adjust anything.

So, go ahead and put the yellow jackets in the outer two positions and flip to the 60 watt position, and you will be in business. I think you will like how it sounds, sort of a Vox AC-15 with more power and more effective tone controls.

Regards,

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#1351302 - 04/02/02 02:57 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5037
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by JamesPeters:
Oh hey I just realised--that's a honkin' tall tube! I may have to change the dimensions of the amp to allow it to fit. What's your KT66 measure--both seated depth (not including the pins, after the bottom of the base) and overall length?
James ...

Just jumping in here even though you were talking to somebody else....

There are now a few KT-66's. The ones that are pretty tall are the copies of the old GEC or Genelux tube from the U.K. The are from China for the most part. They are a hard fit to say the least, but there is also a Sovtek version with a shorter base, that is more of a 6550 style base, with the metal ring. It is a shorter tube, and fits a little easier in more places.

The KT-66 in original form is a big tube. Its a great tube, putting out about 90+ mA at test settings, compared to the 72 mA of a standard 6L6GC. It does require a slightly different bias most of the time.

It will also not fit, unfortunately, in the reissue of the Marshall model 1962 bluesbreaker amp. For some reason when they made this amp, the dropped the cabinet depth from about a foot to about 9 1/2 inches, so how the KT-66, which was the original tube used back then, won't fit. I guess that's no big deal, because with 25% or more less cabinet volume, it already sounds different for other reasons. Thankfully the KT-66 will fit in their JTM-45 reissue.

Regards,

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#1351303 - 04/02/02 03:01 PM Re: Feel free to ask Myles
retroguitarist Offline
Senior Member

Registered: 03/30/02
Posts: 75
Loc: new joisy
hey miles, i got a question for you



or

which one should i buy for you?

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#1351304 - 04/02/02 03:14 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5037
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by fantasticsound:
Hi Myles,

My question was missed, as well. I had difficulty getting internet access on the rest of our Middle East tour, so I had few chances to bump the thread. Here it is.

Neil\'s tube question regarding a Peavey Delta Blues 2 - 10" combo.

Thanks for any assistance you can provide.
fantasticsound...

Answered that over in the link you had here....

Regards,

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#1351305 - 04/02/02 03:22 PM Re: Feel free to ask Myles
sgguitarzz Offline
Senior Member

Registered: 04/01/02
Posts: 91
Myles -

Thank you very much for your quick response. It is much appreciated. You are providing a valuable service for all of us out here.

Dennis

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#1351306 - 04/02/02 05:43 PM Re: Feel free to ask Myles
JamesPeters Offline
Senior Member

Registered: 03/07/02
Posts: 39
Loc: Calgary, Canada
Thanks Myles. I did find a few KT66's locally...apparently they're the larger ones--I'm going to pick them up in a couple days anyway and try them.

Fortunately for me, to make them work in my amps all I have to do is change enclosure measurements slightly, before the enclosure is made...if I need to that is. \:\)
_________________________
http://petersamps.com
Handmade tube guitar amps

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#1351307 - 04/02/02 06:23 PM Re: Feel free to ask Myles
fantasticsound Offline
10k Club

Registered: 04/07/01
Posts: 16867
Loc: Madison,TN, UNITED STATES
Just to clarify, Myles...

The tube that actually glowed was not installed during travel. It was a replacement one of the guitarists had brought. I take it from your answer that we should NOT expect the tubes in this amp to glow? Under all conditions, or should we expect the tubes to warm up over an hour and a half or two hour set? The stock tubes never glowed. I'm a novice when talking tube amps, but I thought most amp tubes glow after the initial warm up time. Is this correct? Am I missing something in your reply?

Thanks.
_________________________
It's easiest to find me on Facebook. Neil Bergman

Soundclick
fntstcsnd

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#1351308 - 04/02/02 08:06 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5037
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by retroguitarist:
hey miles, i got a question for you

which one should i buy for you?
retroguitarist ...

Probably the lower ....

If I was going for the upper one, I'd want to go back to Amsterdam and take the brewery tour, if they still have it. I went on those tours almost every day during part of 1970. They probably don't even have the tours anymore.

Thanks,

Myles

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#1351309 - 04/02/02 08:10 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5037
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by sgguitarzz:
Myles -

Thank you very much for your quick response. It is much appreciated. You are providing a valuable service for all of us out here.

Dennis
Dennis,

You are more than welcome. Some days responses are faster than others. If I am out working away, its sometimes faster, as there is more free time waiting around for folks to show up for sound checks or whatever, as long as there is a phone line handy.

When I am here, I take the emails in between work or waiting for tubes to cool or whatever.

Regards,

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#1351310 - 04/02/02 08:43 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5037
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by JamesPeters:
Thanks Myles. I did find a few KT66's locally...apparently they're the larger ones--I'm going to pick them up in a couple days anyway and try them.

Fortunately for me, to make them work in my amps all I have to do is change enclosure measurements slightly, before the enclosure is made...if I need to that is. \:\)
JamesPeters,

Don't feel bad, the KT-66 won't fit in the THD Univalve either. Andy was thinking of making the cover taller, but thought it made the amp look less pretty, then he considered sort of a dome on the top of the cover, but so far as passed on that idea too.

When I use a KT-66, I just leave the cover off, as it looks like a high end audio amp, the KT-66 is a pretty tube when all lit up, and it also reminds me of the MC-60 and other McIntosh amps of the past, with their exposed tube compliment.

I think your amp looks pretty the way it is. I would not change it. Maybe try the Sovtek KT-66 which is shorter.

Regards,

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#1351311 - 04/02/02 09:11 PM Re: Feel free to ask Myles
JamesPeters Offline
Senior Member

Registered: 03/07/02
Posts: 39
Loc: Calgary, Canada
Quote:
Originally posted by myles111:
I think your amp looks pretty the way it is. I would not change it. Maybe try the Sovtek KT-66 which is shorter.
Oh, the Sovteks are shorter? Right on; those are the ones in stock at the music store anyway.

In any case, if I did have to change the height it would've been more than I wanted to--I'd have to leave at least an inch from the top of the tube to the underside of the top of the enclosure (so the tubes don't smack against the enclosure when you're removing them!) I had looked up the tallest tube that I had planned to use with the amp, the 6CA7 (EL34 equivalent), and based the measurement on its longest overall length plus one inch or so for clearance. I'd almost forgotten about that... \:\)

But I'm still going to try the KT88 and 6550 in it soon. And, if that Sovtek KT66 fits, then for sure I'm giving it a test.
_________________________
http://petersamps.com
Handmade tube guitar amps

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#1351312 - 04/02/02 10:05 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5037
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by fantasticsound:
Just to clarify, Myles...

The tube that actually glowed was not installed during travel. It was a replacement one of the guitarists had brought. I take it from your answer that we should NOT expect the tubes in this amp to glow? Under all conditions, or should we expect the tubes to warm up over an hour and a half or two hour set? The stock tubes never glowed. I'm a novice when talking tube amps, but I thought most amp tubes glow after the initial warm up time. Is this correct? Am I missing something in your reply?

Thanks.
fantasticsound,

If you mean, on an output tube, the outside of the plate structure is glowing, that is bad.

The tube may be faulty, or of a different heat range than what the bias is set for.

If you are talking about inside the tube, some tubes have construction that lends a better look see into the tube and the plate structure on the other side.

Were they the same tubes, the glowing and the non glowing?

Also, if the tube traveled, who knows what may have transpired. Only a good high voltage tube tester or a vacuum tube curve tracer could tell you that.

Regards,

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#1351313 - 04/02/02 10:22 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5037
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by JamesPeters:
Quote:
Originally posted by myles111:
I think your amp looks pretty the way it is. I would not change it. Maybe try the Sovtek KT-66 which is shorter.
Oh, the Sovteks are shorter? Right on; those are the ones in stock at the music store anyway.

In any case, if I did have to change the height it would've been more than I wanted to--I'd have to leave at least an inch from the top of the tube to the underside of the top of the enclosure (so the tubes don't smack against the enclosure when you're removing them!) I had looked up the tallest tube that I had planned to use with the amp, the 6CA7 (EL34 equivalent), and based the measurement on its longest overall length plus one inch or so for clearance. I'd almost forgotten about that... \:\)

But I'm still going to try the KT88 and 6550 in it soon. And, if that Sovtek KT66 fits, then for sure I'm giving it a test.
JamesPeters,

Well, whatever you do, keep me informed. You're doing some great work here.

Myles

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#1351314 - 04/02/02 11:03 PM Re: Feel free to ask Myles
JamesPeters Offline
Senior Member

Registered: 03/07/02
Posts: 39
Loc: Calgary, Canada
Ok, but you're beginning to make me blush! \:D
_________________________
http://petersamps.com
Handmade tube guitar amps

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#1351315 - 04/03/02 04:53 AM Re: Feel free to ask Myles
JamesPeters Offline
Senior Member

Registered: 03/07/02
Posts: 39
Loc: Calgary, Canada
Ok, just tested the 6550 in it (Svetlana 6550C, and 6550B--that I got from the guy who's making my enclosures...leftovers from his Ampeg SVT when he switched to KT88s as it were).

The current draw slightly exceeds the spec for both the power tranny and the output tranny, but just by a hair. 72mA plate current--2mA "extra" for the 70mA rated OT (Hammond 125DSE), and 7mA "extra" for the Hammond 269EX PT (rated at 65mA, so that's not much extra anyway). Given that these Hammond trannies have been known to withstand considerably worse abuse, I'd say it's a go for the 6550. (The trannies didn't even get warm, and I was actually using a 125CSE OT rated for 60mA max. for the test, just to know for sure if the 125DSE would be safe--call me paranoid! \:\) ) Oh yeah, and the heater current draw is still 300mA below what the filament supply is rated for (2.2A instead of 2.5A), so that's a gimme.

The 6550 has a fairly nice sound in this amp, all things considered, which being biased this cold I found surprising (72mA, for a tube which "normally" should see about 140-150mA at this plate voltage--222V B+). It's total heavy metal at this point--really high headroom so the preamp gain "crackle" comes through a lot. It's more forceful and not as bouncy as the 5881, so the envelope is more "square" and abrupt. Not exactly what I had intended the amp to be used for, but hey I'll take it! \:\) Actually, since the plate voltage is browned out that extra amount, it still has a nice warmth to it. I like the woody overtones of 6550s usually--I'll have to check it out my amp cranked with a less overdriven preamp sound, to hear if I can really take advantage of that or not at this bias point/B+. (Hmm, I wonder what triode mode will sound like...)

Talk to you later!
_________________________
http://petersamps.com
Handmade tube guitar amps

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#1351316 - 04/03/02 03:24 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5037
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by JamesPeters:
Ok, just tested the 6550 in it (Svetlana 6550C, and 6550B--that I got from the guy who's making my enclosures...leftovers from his Ampeg SVT when he switched to KT88s as it were).

The current draw slightly exceeds the spec for both the power tranny and the output tranny, but just by a hair. 72mA plate current--2mA "extra" for the 70mA rated OT (Hammond 125DSE), and 7mA "extra" for the Hammond 269EX PT (rated at 65mA, so that's not much extra anyway). Given that these Hammond trannies have been known to withstand considerably worse abuse, I'd say it's a go for the 6550. (The trannies didn't even get warm, and I was actually using a 125CSE OT rated for 60mA max. for the test, just to know for sure if the 125DSE would be safe--call me paranoid! \:\) ) Oh yeah, and the heater current draw is still 300mA below what the filament supply is rated for (2.2A instead of 2.5A), so that's a gimme.

The 6550 has a fairly nice sound in this amp, all things considered, which being biased this cold I found surprising (72mA, for a tube which "normally" should see about 140-150mA at this plate voltage--222V B+). It's total heavy metal at this point--really high headroom so the preamp gain "crackle" comes through a lot. It's more forceful and not as bouncy as the 5881, so the envelope is more "square" and abrupt. Not exactly what I had intended the amp to be used for, but hey I'll take it! \:\) Actually, since the plate voltage is browned out that extra amount, it still has a nice warmth to it. I like the woody overtones of 6550s usually--I'll have to check it out my amp cranked with a less overdriven preamp sound, to hear if I can really take advantage of that or not at this bias point/B+. (Hmm, I wonder what triode mode will sound like...)

Talk to you later!
James,

One thing that might work a bit in your favor, is that on small amps, people tend to drive them at max a lot more often than larger amps.

Most folks think that class A amps draw the same amount of plate current at idle, as they do at full output, but this is not 100% true .... at full output they actually drop a few percentage points (very slight), than at idle.

You will probably be safe, but in the case of output transformers, you don't have much safety margin there. Mos folks in the past put transformers rated at 50 watts in an amp designed to develop 50 watts, and this is the reason for more output transformer failures than one might expect. Today's amps are driven harder than those in the past, musical styles have changed. We also have the issue of things like tubes that fail more easily, and an output tube failure can take out an output transformer at times too. There are also folks that improperly set the output impedience selectors, and with a narrow margin on the transformer, it means a lot less time before there is failure.

A lot of folks now use transformers with a much higher rating than the amp would require from a strict engineering sense, such as Rivera and THD. Maybe talk to the folks at THD, as they may be able to be a great transformer supplier for you.

Regards,

Myles

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#1351317 - 04/03/02 04:01 PM Re: Feel free to ask Myles
JamesPeters Offline
Senior Member

Registered: 03/07/02
Posts: 39
Loc: Calgary, Canada
Thanks again for the tips, Myles. I do think that the 6550 drawing 72mA instead of 70, through the 125DSE, is plenty fine though. To be honest, it's not a "wonderful" sound in the amp anyway--I think the EL34 is nicest, and the 6L6s/5881s have nice definition and are more than adequate for "metal" music. The 6550 is more abrupt and unforgiving with dynamics in the higher gain settings--kinda like solid-state that way (but not really, you know what I mean).

I'm going to sell the amp with the 125DSE by default, and if someone absolutely wants reliability with a 6550 then I'll just put in a 15W 125ESE--they're the same price anyway! \:\)

Talk to you later.
_________________________
http://petersamps.com
Handmade tube guitar amps

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#1351318 - 04/03/02 08:59 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5037
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by JamesPeters:
Thanks again for the tips, Myles. I do think that the 6550 drawing 72mA instead of 70, through the 125DSE, is plenty fine though. To be honest, it's not a "wonderful" sound in the amp anyway--I think the EL34 is nicest, and the 6L6s/5881s have nice definition and are more than adequate for "metal" music. The 6550 is more abrupt and unforgiving with dynamics in the higher gain settings--kinda like solid-state that way (but not really, you know what I mean).

I'm going to sell the amp with the 125DSE by default, and if someone absolutely wants reliability with a 6550 then I'll just put in a 15W 125ESE--they're the same price anyway! \:\)

Talk to you later.
JamesPeters,

Try a 6550C, a Chinese version of the 6550. They have about 20% less output, and a softer vacuum, so they distort a bit more like 6L6's. They also like lower plate voltages, so these may be quite nice in your amp.

If you order some from anybody, tell them you want something that is about the same as a Groove Tubes #2 or #3 rating, as these will draw a bit less current, and also distort a little easier and quicker.

Regards,

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#1351319 - 04/03/02 09:37 PM Re: Feel free to ask Myles
Eddie123579 Offline
Member

Registered: 04/03/02
Posts: 1
Myles - I'm a refuge from the HC amp forum and figured I'd check out your new digs. I have two tube related questions for you.

Background. I have a Rivera K100 head. As backups to the stock preamp tubes which were:

V1 Sovtek 12AX7WB
V2 Sovtek 12ax7wb
v3 Sovtek 12ax7LP
v4 Sovtek 12ax7wb
v5 Sovtek 12ax7lp

I purchased 5 JJ ECC83S.

Because the Sovtek WBs have a pretty crappy reputation, I figured I'd try the JJs in all slots. There was no major improvement to be heard. I love the sound of the amp but I wonder if I'm using it to its full potential.

Question #1. Without putting in expensive NOS preamp tubes, do you have any reccomendations for my amp using the tubes I already have or maybe some other manufacturers such as EH?

Question #2. The stock power tubes are Svetlana EL34's and Rivera has a stamped #7 on the tubes. I was going to purchase some JJ's as backups. Can I purchase tubes from other manufacturers (since I know the rating that rivera uses)that are rated similarly and not have to worry about adjusting the bias on the amp?

Thanks in advance for your advice.

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#1351320 - 04/03/02 11:07 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5037
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by Eddie123579:
Myles - I'm a refuge from the HC amp forum and figured I'd check out your new digs. I have two tube related questions for you.

Background. I have a Rivera K100 head. As backups to the stock preamp tubes which were:

V1 Sovtek 12AX7WB
V2 Sovtek 12ax7wb
v3 Sovtek 12ax7LP
v4 Sovtek 12ax7wb
v5 Sovtek 12ax7lp

I purchased 5 JJ ECC83S.

Because the Sovtek WBs have a pretty crappy reputation, I figured I'd try the JJs in all slots. There was no major improvement to be heard. I love the sound of the amp but I wonder if I'm using it to its full potential.

Question #1. Without putting in expensive NOS preamp tubes, do you have any reccomendations for my amp using the tubes I already have or maybe some other manufacturers such as EH?

Question #2. The stock power tubes are Svetlana EL34's and Rivera has a stamped #7 on the tubes. I was going to purchase some JJ's as backups. Can I purchase tubes from other manufacturers (since I know the rating that rivera uses)that are rated similarly and not have to worry about adjusting the bias on the amp?

Thanks in advance for your advice.
Eddie,

Paul Rivera optimizes his amps for the WB's and in most cases these work really well in his amps. The ECC83's may be a bit of a different sound, so that is all personal preference.

I have a lot of his products, and have swapped things all over the place, but generally come back to his selections.

The most important factor on the preamp tubes, is knowing what is in there, as far as the characteristics of the tube, so you can get about the same gain structure as what you had in there before.

It all comes down to personal preference on the preamp tubes.

On Paul's Svetlana's ... a #7 is, I believe, in his lower range, with something like a #13 at the top. You may want to give them a call and ask, but Paul does do a bit of extra screening on his tubes, so if you amortize the cost over at least a year, it may be the best way to go. If you do get Svetlana's in the same range, then you would not need to re-bias.

My only caution here, would be to stay clear of The Tube Store, as their rating system leaves much to be desired.

Sorry, as this sounds like I have been of absolutely no help.

Regards,

Myles

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#1351321 - 04/07/02 05:39 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5037
Loc: Los Angeles CA, UNITED STATES
Bumping for new folks that may have missed this

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#1351322 - 04/09/02 01:33 AM Re: Feel free to ask Myles
hechtdavid Offline
Member

Registered: 04/01/02
Posts: 26
Hi Myles,

I just started experimenting with changing pre-amp tubes on my 1999 Evil Twin. Got a few JJ's from Bob at Eurotubes and so far so good... I especially like the improved reverb. The overdrive sounds are nice and crunchy, but the new ECC83s in V1 doesn't sound much different than the stock 7025 that it replaced. Here's my question. Since the fx loop never gets used, do I essentially have new tubes in V4 and V7 (the fx send and return)? I'll be doing a few swaps in V1 between the JJ's and the 7025's that came with the amp, so I thought I could swap out the tube in V7 and put it in V1. OK with you? BTW, the old 7025's still sound pretty darn good. Seems to me that they have a lot of life left in them. How often do you change your pre-amp tubes?

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#1351323 - 04/09/02 02:58 PM Re: Feel free to ask Myles
myles_rose Moderator Offline
MP Hall of Fame Member

Registered: 11/28/01
Posts: 5037
Loc: Los Angeles CA, UNITED STATES
Quote:
Originally posted by hechtdavid:
Hi Myles,

I just started experimenting with changing pre-amp tubes on my 1999 Evil Twin. Got a few JJ's from Bob at Eurotubes and so far so good... I especially like the improved reverb. The overdrive sounds are nice and crunchy, but the new ECC83s in V1 doesn't sound much different than the stock 7025 that it replaced. Here's my question. Since the fx loop never gets used, do I essentially have new tubes in V4 and V7 (the fx send and return)? I'll be doing a few swaps in V1 between the JJ's and the 7025's that came with the amp, so I thought I could swap out the tube in V7 and put it in V1. OK with you? BTW, the old 7025's still sound pretty darn good. Seems to me that they have a lot of life left in them. How often do you change your pre-amp tubes?
hechtdavid,

On most amps, depending on if the loop is a series or parallel loop, and a few other factors, you may be able to remove the tubes altogether. This may also allow your amps power supply to be able to provide a bit more plate voltage to the other preamp tubes. This is an old Fender trick, where people either pull V1 or V2 when they only use one of the channels.

So .... yes, feel free to swap.

Preamp tubes last for years, with the exception of the phase inverter or driver tube, which some believe should be changed when output tubes are changed.

Regards,

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