5881's in an Accomplice Jr ?

Drewski

Gold Supporting Member
Messages
1,098
Guys, Ive sent a couple unanswered emails to David Allen, so Im coming here for help.

Ive got a fairly new to me Accomplice Jr. It came with a 5AR4 and 6V6's in it. Id love to try it with 5881's and 6L6's at some point. Do I need to change rectifiers with that change, or simply rebias with the 5AR4? I know it can run the 6L6's, but have no clue if say Tung Sol RI 5881's can happily reside in this circuit.

Any help would be appreciated.

Im very familiar with rebiasing via a trim pot like this amp has, and have done so with various 6V6 changes. So thats not an issue.
 

Blue Strat

Member
Messages
30,201
6L6GCs (the suffix is critical as different suffixes indicated different plate voltage limitations) wouldn't be any problem as long as the transformers support them.

5881s might be ok or not. Generally, if 6V6s are ok with a 5AR4 (the highest voltage output rectifier) then 5881s are ok because they have higher plate voltage capability than 6V6s. If you can measure the plate voltage and it's 450 or lower, 5881s will be ok.

When making the change, set the bias current to the lowest possible setting with your 6V6s first. The 6V6 bias setting will be WAY high for either 6L6s or 5881s.
 

Drewski

Gold Supporting Member
Messages
1,098
Thanks Mike, I shouldve just sent you a pm...

Yeah, the Allen website lists 6L6GC's/6V6 with the same 5AR4 rectifier, so Im assuming the trannie can take it.

Thanks for the tip on the bias setting. That makes perfect sense.

I sold my bias rites so Im just using the amps bias points, and dont know how to check plate voltage with a meter....

Ill try it with the 5881 RIs and see what happens!

Thanks again
 

Blue Strat

Member
Messages
30,201
Better to post here for the benefit of others. It's a forum, right? ;)

You'd have to go inside to measure the plate voltage. Pin 3 on either power tube to ground.
 

mherrcat

Member
Messages
22
I know as of about a week ago David Allen was going out of town, so that may be why you didn't get a reply.

I also have an Accomplice Jr. It also came with 5AR4 rectifier and 6V6's. I bought some Phillips 6L6WGB tubes from Mike and have been using those for several months. I'm still playing around with this amp so I occasionally swap back and forth between the 6L6s and the 6V6s; re-biasing, of course. No problems.

Well, that's not entirely true. I did have a problem about a month ago when the amp volume dropped to almost zero. I sent the chassis to David to check out and he couldn't find anything wrong with it. (There are two threads on the TDPRI forum with details.)

Anyway, the amp sounds fine now and still has the 6L6WGBs in it. I have also tried a couple of different rectifiers; 5V4 and 5R4GYB. I just put in the 5R4GYB in place of the 5AR4 and it sounds fine as well. I have also tried some Winged C 6L6GC tubes and the amp was fine with those as well.

As Mike has pointed out, start with your bias voltage at lowest setting (max negative voltage) which IIRC is measured from pin 5 on the power tubes to ground. (Correct me if I am wrong.) On the Accomplice Jr. you should read between -50 and -60 volts. NOTE: this is not the reading from the bias test points.

Be careful when checking the voltage on those pins. It's easy for those probes to slip! I like to use the little hook-style clips.
 






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