5Y3/6V6s in a 5F6A

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punkykatt
Junior tube assistant
Posts: 6
(4/16/04 8:01 pm)
 5Y3/6V6s in a 5F6A
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Hello all, I want to try 6V6s in my Hoffman homebrew 5F6A. Im presently running 6L6s with a 5U4GB and my B+ is 438vdc. If i install a 5Y3 it should bring the B+ down 25v to 413vdc. The 6V6s should survive but can the 5Y3 cut it? My PT is Dougs #022798. Thanks for your thoughts and suggestions.
Punky
 
PHATamps
I only work on tube amps
Posts: 436
(4/17/04 9:53 am)
 Re: 5Y3/6V6s in a 5F6A
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 A pair of 6V6s wouldn't overdraw a 5Y3; it seems they were made for each other!

I say go for it, but keep in mind that a pair of 6V6s at over 400V likes to see about twice the impedance on the OT primary (6600 to 8500) that 6L6s see in a 5F6-A (4000 to 4200).

Try it as is, you may like it, but (assuming you're using a standard 2-ohm 4-10 cab) if you disconnect two of the RCA speaker plugs from the chassis jacks you'll double the impedance reflected back to the primary for a better match.
 
punkykatt
Junior tube assistant
Posts: 7
(4/18/04 10:23 pm)
 Re: 5Y3/6V6s in a 5F6A
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 Thanks for the reply, sorry for not getting back sooner just spent the weekend in Key West Fl. cellibrating our anniversary.
My OP tranny is from a StrombergCarlson Stereo which origanally used 7027A`s for tubes. The results of my ratio test showed that the primary Z is about 8k and i have three secondary taps 4, 8 and 16. Cant wait to try it Monday morning.
 
punkykatt
Junior tube assistant
Posts: 8
(4/19/04 9:16 am)
 Re: 5Y3/6V6s in a 5F6A
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 Put the 5Y3 and the 6V6s in ,couldn`t adjust the bias to get the mA above 13.3 at 436 plate voltage. I will need to change the bias range resistor. Didnt dare try to play through it with the hi plate voltage.
 
Jeff Flowerday
Senior tube assistant
Posts: 126
(4/19/04 9:46 am)
 Re: 5Y3/6V6s in a 5F6A
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 I run my JJ 6V6s at 450VDC. They are one tough tube.
______________________________________________________
Too many amps? Too many amps my ass!!
 
punkykatt
Junior tube assistant
Posts: 9
(4/19/04 11:48 am)
 Re: 5Y3/6V6s in a 5F6A
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 Jeff, do you think my EH 6V6s will handle 436v? Have you ever used EH 6V6s? What amp are you running those JJs at 450v? and how long have you been running them?
Punky
 
Jeff Flowerday
Senior tube assistant
Posts: 127
(4/19/04 12:24 pm)
 Re: 5Y3/6V6s in a 5F6A
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 Actually when you do get that bias resister changed, the plate voltage will drop as you bring the current up.

I'm guessing 410-420VDC will be your final plate voltage once you get it all biased up. And yes the EHs will handle that much voltage. Though you may want to increase the screen resisters to 1K form 470ohm, EHs are known for weaker screens.

I haven't been running them at that voltage long, but Bob at Eurotubes ran them at 460VDC for 2 weeks of stress testing and they never missed a beat.

I've got them in my Tweed Deluxe, Black Face Deluxe, Princeton, and my Fuchs.

A buddy is running the JJ 6V6s in his bassman with 2 speakers disconnected and a 5R4 rectifier and they are working just fine.
______________________________________________________
Too many amps? Too many amps my ass!!

Edited by: Jeff Flowerday at: 4/19/04 1:51 pm
 
punkykatt
Junior tube assistant
Posts: 11
(4/19/04 1:14 pm)
 Re: 5Y3/6V6s in a 5F6A
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 Thanks Jeff.
Yeah, i was figuring about 415v at the plates when done. Good point about the screens. I was going to change them to 1k for my next experiment with the EL34s.
I was just thinking of putting in a switch so i can switch the values of the bias range resistor. Punky

 
punkykatt
Junior tube assistant
Posts: 12
(4/20/04 8:47 pm)
 Re: 5Y3/6V6s in a 5F6A
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 Nice, very nice works perfect. I changed the screen resistors from 470 ohm to 1k 5 watt, installed a slide type flush mount DPDT switch with the 1k resistor on one side for the 6L6s and a 4.7k resistor on the other side for the 6V6s.
With the tubes im running now i do not need to adjust the bias pot when i make the change.

with the: 5Y3, and 6V6s : 22mA @ 415v plate = 9.1 watts
with the: 5U4GB, and 6L6s : 33mA @ 430v plate = 14.2 watts

For a speaker im using a solid 3/4" oak open back cabinet with a 8 ohm 12" Celestion sidewinder 150 watt speaker.

The amp sounds great both ways.
 
 
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