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Thank you very much for the b'day wishes.

 

__ [font:Comic Sans MS]Soitenly![/font]

 

__ http://www.tdpri.com/telephoto/data/547/medium/3stooges.jpg

Ask yourself- What Would Ren and Stimpy Do?

 

~ Caevan James-Michael Miller-O'Shite ~

_ ___ _ Leprechaun, Esquire _ ___ _

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Hello Myles,

What an invaluable service this thread is! Thanks in advance.

I have a Marshall 4203 Artist with an excessively hot power transformer. The original PT cooked and has been replaced with a Mojotone version of the original Drake. The old PT began to run very hot for a while before it failed. The new PT has run hotter than the old one did before it started getting really hot, so I suspect the old PT did not simply fail - something is maybe drawing more current?

 

The amp has been modded with test points and pots to set bias. I recently retubed with EH EL34s and was unable to open the pots up far enough to get the 43mV which the modder recommended for the GT EL34s that were in the amp when the PT was replaced - I got 32mV. You reference a method of setting bias with a scope and crossover notch method; I've never heard of this method. Is this method described somewhere in this thread? My tech is an EE with multiple scopes sitting around his home studio and he would probably drool at the prospect of finding a new use for his gear.

 

The new PT ran hot with the old GTs installed, and still does with the new EHs. The tubes themselves run reasonably cool, as power tubes go.

 

I'm not extremely knowledgeable about tube amps so I have listened to those who supposedly are, and I have been told:

1. PTs in Marshall 3203/4203 models fail more often than typical in other Marshall models

2. Weak filter cap can cause the PT to run hot.

3. Phase splitter can cause the PT to run hot. (New Mullard 12AX7 on the way)

Do those suggestions sound reasonable?

 

Any help would be much appreciated.

 

Thanks,

 

Chris

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Chris

 

1. PTs in Marshall 3203/4203 models fail more often than typical in other Marshall models

 

Marshalls have weak transformers as a generality in many models, but failure was generally due to running them flat out, not a design issue. Look at the cheap JCM 2000 TSL / DSL transformers for the 100 watt versions and compare the amount of iron to some other 100 watt amps. Heck, the 28 watt Producer has three times the iron. Mercury Magnetics make stuff that will run forever.

 

2. Weak filter cap can cause the PT to run hot.

 

Nonsense.

 

3. Phase splitter can cause the PT to run hot. (New Mullard 12AX7 on the way)

 

Nonsense.

 

Do those suggestions sound reasonable?

 

If you don't run flat out, don't use an attenuator so you can run flat out, and have the proper impedance cab match you will have no more issues than would be found on most amps.

 

Myles S. Rose

www.guitaramplifierblueprinting.com

www.la-economy.blogspot.com

www.facebook.com/mylesr

www.twitter.com/myles111us

 

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Hi Myles,

Thanks for answers. No, I don't run the amp flat out these days, and rarely have in the past, so I don't think I'm taxing the amp in any way.

 

Could you describe the "crossover - notch" bias setting method?

 

Thanks,

Chris

 

That is best shown in real time as my thought on 1k or 400hz, where to set the volume control on the amp (I use 7 on most amps), input setting on the signal generator and what "just goes away" on the notch is personal observation.

 

Get a bias probe. It is more accurate and repeatable.

 

Myles S. Rose

www.guitaramplifierblueprinting.com

www.la-economy.blogspot.com

www.facebook.com/mylesr

www.twitter.com/myles111us

 

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  • 4 weeks later...

Hey again, Myles. :cool:

 

Is there any reason that I couldn't use a Radial Cabbone speaker-switcher connected to one cab to switch a Rivera RockCrusher Attenuator in and out of the path between amp and speaker?

 

That is, having a speaker-cable going from the Cabbone switcher to the speaker-cab from one output, and cable > RockCrusher Attenuator > speaker-cab from the other, perhaps via a parallel/mono Y-cable (speaker cable) connected to each of the Cabbone switcher's outputs...

 

I'd really like to have the attenuator switched-in when switching to the second 'overdrive/distortion/gain' channel of an amp...

 

Thanks once again! :cool:thumbs_up.gif

Ask yourself- What Would Ren and Stimpy Do?

 

~ Caevan James-Michael Miller-O'Shite ~

_ ___ _ Leprechaun, Esquire _ ___ _

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  • 2 months later...

Say, Myles-

 

what are your thoughts on the Egnater Rebel 30 MKII head, which, among other things, uses a pair of 6V6's AND a pair of EL84's, which can be used separately or blended together?

Ask yourself- What Would Ren and Stimpy Do?

 

~ Caevan James-Michael Miller-O'Shite ~

_ ___ _ Leprechaun, Esquire _ ___ _

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Say, Myles-

 

what are your thoughts on the Egnater Rebel 30 MKII head, which, among other things, uses a pair of 6V6's AND a pair of EL84's, which can be used separately or blended together?

 

Personally, I love anything Bruce Egnater has ever done. The designs are terrific and they are very cost effective. As a side note, if you ever want a crash course in amp building / amp repair / amp training, go to one of his seminars. Even if you have to fly across the country and even forgetting that you end up with a door prize .... a great amp that you built yourself in the class .... you still get one heck of an education without going home with student loans to pay off.

 

Bruce Egnater = great stuff = great designs = a great guy too.

 

Myles S. Rose

www.guitaramplifierblueprinting.com

www.la-economy.blogspot.com

www.facebook.com/mylesr

www.twitter.com/myles111us

 

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  • 3 weeks later...

Hello Myles

I would like to ask your advice on re-tubing My mesa quad preamp?

its from 1991 and the original tubes are still in there. Mesa recommended 12spax for 6 spots and just 12ax7 s for 2 (V14 and V24 positions) of them. I want to retain the tone in amp 1, but amp 2 could be a little darker. Just fresh tubes may be the answer but thought i would check.

 

Next question I use a tube works provalve (BK butler) for a power amp with this rig. Can you make a suggestion for 6l6gc replacement tubes to give it bit more head room.

 

 

Thanks for your time.

Lok

 

1997 PRS CE24, 1981 Greco MSV 850, 1991 Greco V 900, 2 2006 Dean Inferno Flying Vs, 1987 Gibson Flying V, 2000s Jackson Dinky/Soloist, 1992 Gibson Les Paul Studio,

 

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  • 2 weeks later...

Please skip this inquiry as I sold the quad that this is in reference too. The one I still own has good tubes, I guess I got everything mixed up when I sold some gear, and switched my whole guitar/bass rig around. I still own the provalve and will be updating the tubes in it eventually, but for now I am using a mesa 20/20 (on loan).

 

Sorry for the question that leads to no where.

 

Lok

1997 PRS CE24, 1981 Greco MSV 850, 1991 Greco V 900, 2 2006 Dean Inferno Flying Vs, 1987 Gibson Flying V, 2000s Jackson Dinky/Soloist, 1992 Gibson Les Paul Studio,

 

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Hi Myles, one of my buddies has an amp question. He has a Mesa Boogie Lone Star head and wants to hook it up to his Rivera K212 B6 speaker cab. The amp has an 8ohm and two 4ohm output jacks. The speaker has two input jacks and the jack plate shows Stereo Z 8 and Mono Z 4.

 

His question is which way to hook up the amp and cab in order to get the best tone while being safe? Should he run from the 2 4ohm outputs on the amp to the two inputs on the cab? or, should he run from the 8ohm output on the amp to a splitter and then plug in to the 2 inputs on the cab?

 

Thanks for any help you can provide! Larryz

Take care, Larryz
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Measure the impedance at the amp end of the speaker cord using various combinations, noting which is at about 3.4 and which is around 7.2 ohms on a DVM. If below 7 ohms use the 4 ohm mesa jack and if above 7 ohms use the 8 ohm jack. The Rivera cabs can be a bit confusing so I always recommend using a ohm meter to assure that things are really as they are expected.

Myles S. Rose

www.guitaramplifierblueprinting.com

www.la-economy.blogspot.com

www.facebook.com/mylesr

www.twitter.com/myles111us

 

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Hi Myles, one of my buddies has an amp question. He has a Mesa Boogie Lone Star head and wants to hook it up to his Rivera K212 B6 speaker cab. The amp has an 8ohm and two 4ohm output jacks. The speaker has two input jacks and the jack plate shows Stereo Z 8 and Mono Z 4.

 

His question is which way to hook up the amp and cab in order to get the best tone while being safe? Should he run from the 2 4ohm outputs on the amp to the two inputs on the cab? or, should he run from the 8ohm output on the amp to a splitter and then plug in to the 2 inputs on the cab?

Measure the impedance at the amp end of the speaker cord using various combinations, noting which is at about 3.4 and which is around 7.2 ohms on a DVM. If below 7 ohms use the 4 ohm mesa jack and if above 7 ohms use the 8 ohm jack. The Rivera cabs can be a bit confusing so I always recommend using a ohm meter to assure that things are really as they are expected.

 

Do I understand correctly, that this Rivera speaker-cab must have two 8 ohm speakers wired in parallel to a TS plug for 4 ohms at the "Mono Z 4" jack, and individually wired to Left and Right TRS plug at the "Stereo Z 8" jack?

Ask yourself- What Would Ren and Stimpy Do?

 

~ Caevan James-Michael Miller-O'Shite ~

_ ___ _ Leprechaun, Esquire _ ___ _

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Thanks Myles, I'll pass that info on with regard to the amp out and the cab.

 

Not sure how it's wired or if it uses a TRS Caevan, as he could not locate a manual for the cab. A Rivera salesman responded to an email suggesting he use the mono side...but, I think he should take a peek under the hood first as the amp manual shows all of the compatible speaker combos...

 

 

Take care, Larryz
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It's easier just to measure the cab and know the actual operation. If you don't have a DVM you can buy one for less tha $10 at any electronics store or online at Amazon. Everybody should have one lying around.

Myles S. Rose

www.guitaramplifierblueprinting.com

www.la-economy.blogspot.com

www.facebook.com/mylesr

www.twitter.com/myles111us

 

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  • 3 weeks later...
  • 3 weeks later...

Myles,

 

Is it safe to have the bias set at 37mA for a Quiana Reverb Studio? I switched techs for my last set up and he set it to 37mA instead of keeping it at 35mA where it usually is set to. It seems to have lost some sponginess in both channels. Is that a symptom of being over-biased? I'm thinking of having him reset it. Please let me know.

 

Thanks,

 

Dave

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Dave,

 

This is totally fine. You are still well within spec and if you prefer the tone that is the main criteria.

 

Actually, the amp would technically be considered under biased compared to 35mA as it is running a bit hotter.

 

 

 

Myles S. Rose

www.guitaramplifierblueprinting.com

www.la-economy.blogspot.com

www.facebook.com/mylesr

www.twitter.com/myles111us

 

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Myles,

 

I'm going to have my tech set to back to 35mA. I really do notice a difference in feel and tone with the 2mA increase, which surprises me. I believe you recommended 35mA for this amp in a previous conversation I had with you.

 

Thanks for your help,

 

Dave

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2mA means almost nothing. If it sounds better, keep it at 37mA.

 

If you send me your plate voltage (measured), I will figure again.

 

Myles S. Rose

www.guitaramplifierblueprinting.com

www.la-economy.blogspot.com

www.facebook.com/mylesr

www.twitter.com/myles111us

 

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Myles,

 

It turns out my tech was testing my amp through a 16 ohm cab and forgot to switch it back to 8 ohms. I played through it three times that way at low volume settings and noticed a pretty big difference in feel and tone from what I was used to.

 

1) Could this have damaged the amp? I haven't picked it up yet since I took it back to him.

 

2) He thinks the speaker ohm setting probably accounted for the change in feel and tone I noticed. Do you agree?

 

3) Do you recommend biasing Quianas at 35mA?

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  • 2 months later...

Greetings Myles

This is my first question in ages-I have a VHT Valvulator, which is basically a line buffer-the manufacturer recommends a Sovtek 12AX7WB as the proper tube, but I just got my second replacement tube and, somewhere along the line-I don`t know if it`s my fault for grabbing the wrong tube off the shelf (previously) or the music store guy needs glasses (the new one), but they called and told me my 12AX7WA tube had arrived. I thought, uh oh. I looked on the receipt and sure enough, the guy wrote 12AX7WA. I saw a chart which shows about a 10% loss of gain with the WA and it is not the best choice for an amp-but is it a problem for the VHT? I have a recording session in two days so I`m not going to go back to the store at this point.

Same old surprises, brand new cliches-

 

Skipsounds on Soundclick:

www.soundclick.com/bands/pagemusic.cfm?bandid=602491

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Myles,

 

It turns out my tech was testing my amp through a 16 ohm cab and forgot to switch it back to 8 ohms. I played through it three times that way at low volume settings and noticed a pretty big difference in feel and tone from what I was used to.

 

1) Could this have damaged the amp? I haven't picked it up yet since I took it back to him.

 

2) He thinks the speaker ohm setting probably accounted for the change in feel and tone I noticed. Do you agree?

 

3) Do you recommend biasing Quianas at 35mA?

 

Rivera stuff have stout transformers. I would guess there is not an issue. 35mA is fine but if you send me the actual B+ I will send you a 10% range.

 

There really should have been not much of a perceptible level change in volume when going from 8 to 16 ohms using the same cab. If there is, then I'd investigate further with your amp tech or ask him explain why.

 

 

Myles S. Rose

www.guitaramplifierblueprinting.com

www.la-economy.blogspot.com

www.facebook.com/mylesr

www.twitter.com/myles111us

 

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Greetings Myles

This is my first question in ages-I have a VHT Valvulator, which is basically a line buffer-the manufacturer recommends a Sovtek 12AX7WB as the proper tube, but I just got my second replacement tube and, somewhere along the line-I don`t know if it`s my fault for grabbing the wrong tube off the shelf (previously) or the music store guy needs glasses (the new one), but they called and told me my 12AX7WA tube had arrived. I thought, uh oh. I looked on the receipt and sure enough, the guy wrote 12AX7WA. I saw a chart which shows about a 10% loss of gain with the WA and it is not the best choice for an amp-but is it a problem for the VHT? I have a recording session in two days so I`m not going to go back to the store at this point.

 

There is no right or wrong, it is all personal preference. Both the WA and WB are cheap, low gain, but sturdy tubes. If it were my unit I'd go NOS and used a tube that meets spec rather than one that surely is not even close.

 

Myles S. Rose

www.guitaramplifierblueprinting.com

www.la-economy.blogspot.com

www.facebook.com/mylesr

www.twitter.com/myles111us

 

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Greetings Myles

This is my first question in ages-I have a VHT Valvulator, which is basically a line buffer-the manufacturer recommends a Sovtek 12AX7WB as the proper tube, but I just got my second replacement tube and, somewhere along the line-I don`t know if it`s my fault for grabbing the wrong tube off the shelf (previously) or the music store guy needs glasses (the new one), but they called and told me my 12AX7WA tube had arrived. I thought, uh oh. I looked on the receipt and sure enough, the guy wrote 12AX7WA. I saw a chart which shows about a 10% loss of gain with the WA and it is not the best choice for an amp-but is it a problem for the VHT? I have a recording session in two days so I`m not going to go back to the store at this point.

 

There is no right or wrong, it is all personal preference. Both the WA and WB are cheap, low gain, but sturdy tubes. If it were my unit I'd go NOS and used a tube that meets spec rather than one that surely is not even close.

 

Kool-so aside from manufacturer`s recommendation-and keeping in mind it`s not an amp-how would you determine the best choice? unfortunately the unit has been discontinued-I don`t know if there`s enough tech information available to brave the NOS waters.

BTW thanks for the reply.

Same old surprises, brand new cliches-

 

Skipsounds on Soundclick:

www.soundclick.com/bands/pagemusic.cfm?bandid=602491

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