Last word on Sovtek 5881 plate voltages, pleeeeeease.

[carryonplease]

hi guys! i hope some of you who posted in this thread are still around. I have been running JJ6L6s in my red bear mk 60 for about 3 months now and i think i want to try something different. To MY ears, the amp is still pretty harsh, and it only really cuts in the lows and highs in a band setting, and i want beefier mids. I am assuming the plate voltages on my amp are around the same as the guy who mentioned his, although i have never measure them. I also haven't really properly biased the amp, only messed around with the bias pot with the amp on seeing what i like best, and the bias pot is currently around 3 o clock or so, so the tubes are running pretty hot.

How easy would it be for this amp to take EL34s. That is basically what I am looking for. Or could there be a 5881/6L6 replacement that would be safer? I have done slight modifications on this amp so i would be able to do more if getting EL34s to run was easy.

[Chuck H]

El34's will give you a mid hump compared to 6L6's. I don't know how the power tube sockets are wired in that amp, so it's up to you to determine if EL34's are a plug and play tube (with bias adjustment of course. This may require one resistor change in the bias circuit). Just look at how your sockets are wired and pay attention to internal pin connections. Any mod to retrofit your amp to accept EL34"s should be easy. But, as I stated in a previous post on this thread, I'm not sure about the current capacity of the 6.3V PT secondary wind. I say (provided the sockets are wired correctly) plug in a pair of EL34's and bias it up. If the heater voltages don't sag and the PT doesn't get too hot you should be fine. Reading your post I think you would be happier with the EL34's if they can be made to work.

Chuck

[carryonplease]

thanks chuck,

from my research about the amp i think i will have to mod the bias trim pot. according to what i've read and also what i've heard the bias pot has a very small range, only about 10k i've read. I would assume in order to properly bias EL34s i would have to work with the bias pot.

im not so much worried about the mod at this point. I am just wondering how I am going to find out if my transformer can handle the extra filament draw. There are no spec sheets and zero information about the transformers in these amps, other than the fact that the look pretty beefy.

I would assume since it is only 2 power tubes i am working with, that i safer than 4. but is there some kind of probe or kit i can use to test this?

[Enzo]

Plug the tubes in the sockets and see if the 6V drops. if it handles the extra current, then it will work.

DOn;t modify your bias first. Stick a voltmeter in an empty power tube socket and measure pin 5. If a 6L6 gets about -50 to -55 say, then your EL34 will wany more like -40 to -45. What does the adjustment give as a range of voltages? If the bias voltage goes low enough, then it is already set. That the adjustment pot is "only" 10k doesn't tell us anything. That is only meaningful in the context of the rest of the circuit.

You will want to install screen resistors, typically 1k 5w.

And EL34s need pins 1 and 8 wired together. MAny 6L6 amps use pin 1 as a convenient solder terminal, so make sure pin 1 is free to be connected to pin 8.

[carryonplease]

are you saying i can plug in EL34s without modifications? That doesn't make sense, they have a different pin out?

What do you mean by "if the 6V drops?" Please explain this if you could.

I think i will want to make the bias pot have more of a range anyway first because i could quite possibly be runnning my 6L6s cold and i might just be happy with them running hotter. I still have yet to get any real readings so I will do that when i get a chance.

[Alex R]

Perhaps I might presume to offer some explications.

are you saying i can plug in EL34s without modifications? That doesn't make sense, they have a different pin out?

Enzo wrote:

"You will want to install screen resistors, typically 1k 5w.... And EL34s need pins 1 and 8 wired together."

These are modifications.

What do you mean by "if the 6V drops?" Please explain this if you could.

You can tell whether the heater winding can take the extra current draw EL34s require by plugging them in and watching whether the heater voltage holds up.

[Enzo]

What Alex said.

I specifically said don;t modify the BIAS first.

Right or wrong, it sounded to me like you planned to start changing bias supply resistors before finding out if the existing circuit had range enough already. I was suggesting you find out first.

[carryonplease]

yea, i'm almost positive that is doesn't have a large enough range, from reading this website.

ringomedia.net - sankt-peterburg tube laboratory

He is talking about the 100 watt version here i believe

"The amp has a bias trimmer installed internally and interestingly the maximum idle plate dissipation I could set it to was about 16.5 Watts per tube. Seems there is no way to bias the tubes too hot without mods. The bias range I get from the trimmer is very small (it's only a 10k trimmer). I suppose this would be easy to change but I left it for now."

[rockon1]

The Sovtek 5881WXT is as close to indestructable as they come in guitar amps. Theres a reason they are the stock tube of choice in so many mass produced amps. Come to think of it Ive yet to have one fail on me in any of my amps. Bob

[Alex R]

I just put a pair in an Ampeg VT40, to replace the 7027As. Talked it over with the customer beforehand, saying they would probably hold up but I couldn't guarantee it. I had switched the amp over to EL34s previously, but he didn't like the sound. Anyhow, 595vDC on the plates, idling at 15W per tube and not a crackle or a pop in an hour. They seem like happy tubes to me. Now don't take this as a recommendation or anything, but still...

[Albert Kreuzer]

Fender ran them at 35W idle in a stock Prosonic. No problem, no redplating.
Tubes were tired after two years of daily use (several hours/day).

Cheers,
Albert

[Alex R]

- all that and they're cheap too. FGS this is the internet, write something bad about them or they'll be 50 quid apiece before you know it. You know, they destroy your soundstage or compromise your touch-sensitivity or something.

[Nigel]

I've had a Zinky Mofo amp for 7 years. It came with the wafer-base Sovtek 5881's.

The amp has ALWAYS had a sharp, shrill upper midrange that cannot be tamed.

I'll not bore you with the experiments, but the screen resistors have been upped from 470 ohms to 1K/5W.

The tubes are biased 535V/55MA (the hot one) and 535/50MA (the cool one).

It's like 27.5/29.5 watts at idle! However, the TOANZ! OMG!

NEVER would have believed these things could sound SO GOOD!