Archon 25 EL34 bias question?

[BC82]

My archon had 5881's that were both dead on 30mV. I just put in some new Mullard El34's and after adjusting, the bias pot is maxed. One tube shows 27.6 mV and the other, 24.7mV.

Is this a huge deal being that they are supposed to be 30mV? This is my first tube amp I've had to bias and I'm not sure. Thanks for any help. I've browsed elsewhere for answers and could not find any.

 

[AP515]

They'll just be running cold. They won't sound as good as they can. You should let the tubes warm up a few minutes before you check them. They will probably be closer together when warm unless they are not a matched set. You might try a matched set that breaks up early. They might get to 30 before you max out the pot. Just a guess though. Somebody that knows more might give you better advice.

 

[BC82]

They'll just be running cold. They won't sound as good as they can. You should let the tubes warm up a few minutes before you check them. They will probably be closer together when warm unless they are not a matched set. You might try a matched set that breaks up early. They might get to 30 before you max out the pot. Just a guess though. Somebody that knows more might give you better advice.

Thanks for the reply. They've got about an hour on them now and running about the same mV. I bought them as a matched set. I read that within 2-3 mV for matched is fine. I'm no pro, so I'm not sure.

The sound isn't all the way there for me anyways. I'm gonna let them cool and try the Tung-sol 5881's again. See which sound better to my ears. The EL's were definitely a lot brighter.

 

[elvis]

I suspect that you may have impedance issues. The EL34 can be swapped into the 6L6 amps, but I don't know how compatible the output transformer of a 5881 amp is with EL34. That essentially makes a 25W amp into a 50W amp, which may be too much for it.

I'd definitely check with PRS about the advisability of this swap.

 

[shinksma]

I don't know much about tubes, so this thread interests me because it makes me dig a little and read-up on the various types.

I found this:

http://www.thetubestore.com/Tubes/6L6-5881-Tube-Types

The 5881 power tube is a 23 watt version while 6L6GC and 7581 vacuum tubes are 30 watt. These different variations also have different plate voltage limits.

And this:

https://www.sweetwater.com/insync/5881-versus-6l6-tubes/

In tech terms, 5881 tubes generally have smaller plates, which are not able to withstand plate voltages as high as 6L6 tubes can tolerate. This results in 5881 tubes having less outputpower than a 6L6 (how much difference depends on the specific tubes) and also lower cleanheadroom, meaning a given 5881 may start to distort at a lower level than a given 6L6.

So, from reading that, if the amp comes with 5881s, putting in EL34s means the EL34s probably won't be driven as hard as they might in a different amp, but it won't damage the amp, as long as the bias voltage is tweaked properly. Now maybe for the Archon 25 the bias cannot be adjusted sufficiently for EL34s, or maybe those settings are OK but the EL34 simply isn't coming alive. Keep in mind the EL34 will sound "less bassy", so maybe that's why the OP doesn't like the result. I saw this description, which might help (I have no idea how accurate it might be, and perception is a filter all on its own):

The 6l6's had more bass and more of a grain/grind to em.

The 34's have a bit of a non grainy crunch to them and are a bit more articulate.

 

[Buildermike]

I'd suggest you send an email to the PTC.

 

[bodia]

I don't know much about tubes, so this thread interests me because it makes me dig a little and read-up on the various types.

I found this:

http://www.thetubestore.com/Tubes/6L6-5881-Tube-Types



And this:

https://www.sweetwater.com/insync/5881-versus-6l6-tubes/



So, from reading that, if the amp comes with 5881s, putting in EL34s means the EL34s probably won't be driven as hard as they might in a different amp, but it won't damage the amp, as long as the bias voltage is tweaked properly. Now maybe for the Archon 25 the bias cannot be adjusted sufficiently for EL34s, or maybe those settings are OK but the EL34 simply isn't coming alive. Keep in mind the EL34 will sound "less bassy", so maybe that's why the OP doesn't like the result. I saw this description, which might help (I have no idea how accurate it might be, and perception is a filter all on its own):

If you're looking for some good tube info, check out this site:

http://www.audiotubes.com/

It's an old school website, and not very pretty, but there is a ton of good info here.

 

[shinksma]

If you're looking for some good tube info, check out this site:

http://www.audiotubes.com/

It's an old school website, and not very pretty, but there is a ton of good info here.

Cool, was looking for something to read over lunch!