Gabriel E.

Thanks!

Myles, I understand the importance of using a balanced dual triode for a phase inverter if the splitter is of the Shmitt(sp?) type found in most Fender and Marshall-type amps. In these amps, the two halves of the PI basically run in parallel. However, my Super uses a concertina type where the two halves of the PI run in series. What's to be gained [pun intended ] by using a balanced PI in this situation? Thanks, Gabriel

Thanks Myles!

Hey Miles, In your primer, when you talk about biasing using the current draw method, you advise against "chasing the bias" (which I've admittedly been doing) as the wrong current draw can damage the tube before you have a chance to set the bias properly. You go on to suggest lowering the current draw as much as possible before installing the tubes and then bringing it back up to the correct setting once the new tubes are in place. My question is this: If you drop the bias current way down, aren't you pushing the plate voltage way up? Won't this potentially damage the tube as well.

Thanks! I'll let you know how it turns out.

Hi Myles, I am in the process of restoring an old Lowrey Holiday organ from the early 60s that uses 7591 tubes. These tubes are rare and expensive. I've heard bad things about the new Sovtek 7591 tubes (plus they won't fit without poking through the back panel). THD makes a set of conversion Yellowjackets but they will cause the EL-84s to stick WAY out the back panel. And they cost $$. I have received a lot of mixed messages regarding whether I can sub 6L6 tubes if I rewire the sockets (easy to do on this unit). Can the 6L6s handle the voltage? Looking at the specs, it looks like KT66s are closer. Can I rewire and use 6V6s? Thanks in advance for your help. Gabriel

Thanks for the responses guys. Interesting about Curtis Mathis. Never seen one of those TVs around. Bluestrat, I'll PM you a list this evening or tomorrow. Gabriel

Not a question this time - just bragging. Bought a box of tubes at a Salvation Army auction the other day for $25. Most were RCA tubes for B&W TVs. However: 1-Mullard 12AX7 1-Ratheon 5U4GB 1-RCA 12AU7 1-RCA 5R4GYB 1-Amperex EF86 1-Mullard 5AR4/GZ34 with a metal base. All in unused condition. Put the RCA 12AU7 and the Mullard 5AR4 in my tweed Super and it sounds incredible. Need to rebias though cuz the plates on the output tubes started glowing. A bunch of the RCA tubes were rebranded "Curtis Mathers". Know anything about these?

Did some work on my Mig-50. Recapped it and increased the power supply filtering (not as easy as it sounds - couldn't find replacements for through-hole Russian can caps so I had to figure out how to stuff in six 350v Sprague Atoms. Ended up buiding a new circuit board and floated it over the PT bell). Also added a cathode bypass cap to V2. So now the question is which power tubes to put in there. I have decided to stick with 5881s. The amp puts 520 volts on the plates which is more than most 5881s and 6L6s are rated for. I am looking for easy break-up. Would JAN Phillips 6L6WGBs be a good choice?

Ok. Here's another question: When played clean, my Sovtek Mig-50 has a much faster response than my Fender 5F4. I'm assuming this is because of the sag from the 5V4 rectifier in the Fender. Is this the case? If so, what tube(s) would you recommend to speed up the attack? The tube chart specifies a 5U4G but that won't fit since a former owner cut the amp into a head. Thanks

Thanks Myles. Component selection always makes my head spin. New Sensor/Sovtek carry both LCR and JJ caps. Any preference? Also, Allied has some Mallory CGS computer-grade caps for a reasonable price. Is there a noticable difference between these 3 brands? On Ampage, someone mentioned increasing the plate resistors on the preamp tubes to 220K for added gain. Will this work? Worth it? BTW, I switched out the ceramic disks on my Champ 12 for silver micas and replaced the Illinois preamp electrolytics with Black Gates and the thing sings! The tonal improvement is massive. It never ends!

Here's a question re: power supply filter caps. My Sovtek Mig-50 uses two large can-type 200uf/350v electrolytics. I would like to replace them but am finding lots of 220uf caps and not too many 200uf caps. If I use 220uf caps, will the extra 20uf make a difference? BTW, the schematic I found calls for 220uf caps. There are a lot of differences in the pot and cap values between the schem. and the amp.

Can I put EL34s in a Sovtek Mig-50 in place of the 5881s? It supposedly puts over 500V on the plates but the tube data sheet I read for the EL34 said it can handle 800V. Is this accurate? How will the sound differ with EL34s vs. 5881s?

The Solens are rated at 400 and 630 volts. Solen The restaurant you mentioned is probably Cafe Degas. Just ate there last month - Yum! It's in my neighborhood. As is the place you stay which is right by the Rastafarian church.

I'm still a little confused about the Solens. I hear what you're saying about polarized electrolytics normally being used as power supply filter caps (that's what my amps currently have). However some boutique manufacturers such as Carr boast of using Solen Polypropylene filter caps. ?? In the parts list for the single-ended 6v6 project amp at Angela Instruments thay suggest subbing a Polypropolene for a 16uf/475v electrolytic. We've been meaning to go there for a while. The owner/executive chef was a cutomer of mine a few years back. It was a big deal when she opened it because she was only 30 at the time. She made it onto the cover of Wine Spectator too. Next time you're planning on coming to town, let me know. I know some cool places to eat.