Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: rdrgtr on October 28, 2010, 09:00:07 pm

Title: 7027 to 6L6
Post by: rdrgtr on October 28, 2010, 09:00:07 pm

I just scored on an Altec 342b mixer amp.  It even has the 4 mic transformers with it (peerless 4722...very cool and sought after).   I would love to sell the mic transformers in pairs (tube hi-fi guys love these little trannys for phono step ups) and keep the mixer amp for tinkering.  My question is, is there a good substitute for the 7027 output tubes?  I looked at the schematic and could probably rewire the sockets but would like to keep it original if at all possible.

Thanks,

http://tdsl.duncanamps.com/show.php?des=7027

http://www.greatplainsaudio.com/vintage_altec/342B_mixeramp_oper_inst.pdf

Title: Re: 7027 to 6L6
Post by: dude on October 28, 2010, 09:11:31 pm

I went from 7027 to 6550s with good results, same pinout. More headroom by far.

al

Title: Re: 7027 to 6L6
Post by: rdrgtr on October 28, 2010, 09:20:38 pm

thanks dude,  I think I have a couple of those lying around.

Title: Re: 7027 to 6L6
Post by: dynaman1 on October 28, 2010, 10:49:43 pm

http://www.triodeel.com/7027.htm

Title: Re: 7027 to 6L6
Post by: PRR on October 29, 2010, 12:51:13 am

Watch the extra G2 connection on 7027 pin 1. (Do not trust the schematic, LOOK inside.) If the chassis has that pin tied to +400V it can be disastrous with other tubes.

Other than that 7027 is nearly the same as 6L6GC so you can use any guitar-market "6L6".

Title: Re: 7027 to 6L6
Post by: PRR on October 29, 2010, 12:56:29 am

GROUND the chassis.

Be SURE you have -40V bias on output sockets' grids.

Increase R33 to maybe 470K.

Rip all the mix-crap off V3 pin 7 (grid) and build a standard gitar input network. It'll work.

Title: Re: 7027 to 6L6
Post by: triode on October 29, 2010, 05:56:58 am

Ahem, yes, if you are going to sell those 4722s, uhh, PM me first please. I got a TT begging for
them right now.   :grin:

Heed PRRs advice on the 7027 pin out. And yes, a 6L6GC is a good sub.

Title: Re: 7027 to 6L6
Post by: rdrgtr on October 29, 2010, 09:09:23 pm

I just popped it open to take a peak inside.  It appears that nothing is terminated on pin 1 or 6 on both tubes.  I guess it is good to go.  Has anyone had good luck with  the old  peerless iron?  Thanks for the help guys.  This forum has never failed to answer my questions quickly and accurately. 

Title: Re: 7027 to 6L6
Post by: LooseChange on October 29, 2010, 10:14:03 pm

JJ's brand 7027 and 6L6 are identical inside the glass. Just saying.

Title: Re: 7027 to 6L6
Post by: PRR on October 30, 2010, 12:40:28 am

> good luck with  the old  peerless iron?

That's awful stuff. You should take it out, carefully, and ship it to me.   :evil1:

Seriously (since I have no immediate need for very good 35W iron), it might be "too good for guitar". OTOH, I also think the OT in a Ampeg VT40 is "too good for guitar", and nobody notices.