How best to run a pair of cathode-biased 6V6s?

[dehughes]

I'm looking at a couple of different transformers from Mercury Magnetics and am stuck between the typical Tweed PT (380-0-380...but not as "stable") and a more hefty Brown or Black PT (340-0-340, and heftier than the Tweed...). Part of me thinks that I should just go with the Tweed even though it has higher plate voltages and will squish more when the amp is pushed, but then the other side of me thinks that a lower but more stable secondary voltage would provide me with more options. I guess some context is in order...

I'm going to build what is essentially a 5E3 Deluxe but with a second channel (much like the Fargen Tweed-ish amp...), but the second channel is going to be a 6SN7 based one. So, the amp will have low and lower gain channels... Since I have limited experience with the Tweed Deluxe (more familiar with Brown/Black Deluxes....) I'm wondering what type of PT would set me up for more success given the preamp tubes in question, and given that I want the amp to essentially be a lower-volume, studio/small gigs/church amp that lets me turn it up a bit more and get some fun happening.

Would a weaker PT like the stock 5E3 tranny be the better bet for this, or should I go with a bit more hefty PT and tweak the circuit instead? Or, have I set up a false dichotomy?

Thanks!

[CaseyJones]

Mercury's "typical tweed transformer" is 380-0-380? That's high for a tweed Deluxe.

MM commentary: I can see where people might be confused by Mercury's diverse offerings. They build iron that's exactly right for a particular amp which makes it incorrect for anything beside the application it's designed for.

There are lots of very good "tweed Deluxe" transformers from other manufacturers that are excellent for experimentation. For my money I'd buy one of the "generic" replacements that may feature availability of increased current, a 50 volt bias tap or tapped high voltage windings. They sell for about half of what Mercury's premium product sells for. You end up with the option of easy fixed bias if you want it, the correct voltages for a replica Deluxe Reverb if you want them plus the increased current gives you the option of using 6L6s, 5881s or other octals if you want them.

You then have the option of tweaking voltages with rectifier selction. Planning ahead will get you what you want later even if you don't know what you want to begin with.

I don't know why you'd want to use 6SN7s unless you have a lot of them. They're useful if you have very high input levels but not much fun for guitar IMHO.

If you built your project on a 5C5 chassis with two octal to mini converters you'd have a slick package with room for your 6SN7 experiment.

[dehughes]

Thanks for the info. 380-0-380 seemed high, but that's what I was told for their FTDP. I'll ask Paul again just to be sure.

I'd thought about a fixed bias setup, but I'm quite impressed with what one can do with a cathode biased 6V6 pair, so I'm going to go that route for this build. The next one will probably be a fixed bias power section with multiple options for power tubes...

As for the 6SN7...well, I've heard what can be done with that tube in guitar amps (I'm thinking of the Komet Constellation, mostly...) and am just plain curious to see what I can get out of it. Could be lame....could be cool....we'll see. I'd thought about a 6SL7, but figure I'd stick with low mu values (12AY7 and below) in this amp. We'll see.

[rfgordon]

I've done several 6V6 duet powered amps, and have used different transformers--Weber, Heyboer, Musical Power Supplies, to name a few. All the PTs I've tried work well enough, so there's no clear winner for me there. I will say, however, that I get the best (to my ears anyway) tone with 405 VDC on the plates, a tweed-style choke, and about 395 on the screens.

But, I should add that I have a good source for vintage tubes, which is what I use most and sell with my amps. I've got some that are branded for General Motors! Man, when was the last time GM put a tube radio in a car?

I will say that the best bang for the buck are Matt's trannies from www.musicalpowersupplies.com. Very nice stuff.

[dehughes]

Well, Paul just confirmed that their Tweed Deluxe OT (FTDP) is indeed rated at 380-0380 unloaded, FWIW.

Does that seem high for your average 5E3 PT?

Rich, is your setup a fixed or cathode biased one?

[rfgordon]

dehughes,

All my 6V6-powered beasts have been cathode bias. For that voltage (405 VDC) I use a 250 ohm/25 watt resistor and a 100 mF bypass cap. FWIW, I bolt the resistor to the back chassis wall and locate the cap elsewhere. Those resistors get REAL hot.

Also, in my bigger, dual 6L6 amps, I like a similar voltage profile, so the 6V6 & 6L6 are interchangable with only a swap and a speaker jack change.

I think 6V6s in particular sound best cathode bias.

I'm designing a neat amp for a guy that will run a pair each 6L6 and 6V6, to get the top/bottom of the 6L6 and the mid range grind of the 6V6. When he comes across with the cash and I start meltin' lead, I'll post pics.

[dehughes]

Sweet. Thanks. That was my general idea for the bias resistor and cap. I used some 25 and 50w aluminum housed chassis mount resistors in my AC30 and they worked really well for Rk.

I'm inclined to use just the "typical" 5E3 power section for this build, unless someone recommends something otherwise for a cathode biased 6V6 pair. I've had good experiences in the past with amps using similar power sections...but different preamp sections.

[dehughes]

So I'm a dunce...of course the 5E3 PT would kick out 380-0-380, as it will be running into a 5Y3....so in order to get the voltages up after the recto you'd need more BEFORE the 5Y3. If it was a 5AR4 it would be a different story... Man, I need to sleep more and think more...

So, I suppose it's just a question now of picking what PT at what voltage to use, given that I'm going to be using a 5AR4 instead (though still cathode biasing the 6V6s) and putting in more Brown Deluxe in the preamp than 5E3 Deluxe. Yeah, I'm still in the "make up your mind" phase of this build.

Thanks!