grommes 20lj - picking up tomorrow

Caps are done and a few key resistors. Plays but one channel is stronger than the other. I have not sprayed deoxit in the pots because I read somewhere it wrecked the pots on this unit. Wil go through it again tomorrow.
 
After cleaning the pots, you could check all the voltages against those on the schematic too? (If they are given.) That might give you a clue as to where the problem lies.
 
Well, one of the output transformers was half toast meaning it it was totally toast. I could have gotten the originals rebuilt but 360 usd was not going to happen. I got slightly larger new ones from transcendar and had to modify the chassis a bit. One of the fine techs in the tube world was kind enough to put a total recap kit together for so thats all done. It runs nice and cool with the correct voltages but I am having issues with pots and resistors I think. The right channel has the bass boosted and the pot wont affect it. Also when the volume is at zero you can still hear music and it hums a bit with the volume all the way up with no signal. Lastly with a signal to the aux input you can still hear it ghosting then you select a different input. Looks like more work needed. Its a perfect unit to learn with as its very simple. I will probably completely rebuild this unit now.
 
Thanks Dandy. Its really fun and people have been very patient with my fumbling around for the most part. Got a bunch of books and have access to an oscilliscope, a signal tracer and a tube tester. Lot to learn.
 
Been a while since I worked on this unit but I did finish the recap and get it running well and it sounds really good. Much better right now than a Fisher 400 I just picked up. I will post some pictures at some point to show how I mounted the new OT's etc. I also replaced the balance pot, the volume pot still needs replacement as an upgrade.

One thing as I was listening again after getting a pair of Tele 12AX7's in it and putting some RCA's in the phone section is that there is a very low frequency hum which does not react to the volume pot. In fact, with Aux input selected and an IPOD connected not playing anything, its dead quiet on full volume, just the underlying low frequency hum.

To revisit the failure mode on this unit, the original OT's were fried and the PT got so hot that waxy goo leaked out and contaminated two of the EL84 sockets. Those sockets might still have some waxy residue in them but the unit is balanced and sounds good other than when music is not playing. Is it possible that the PT, though still doing its duty is causing this hum due to missing some of its potting material? I hope I can get this sorted out because it sounds great.
 
I just noticed I put a three wire power cord on it. I am going to try disconnecting the connection to the chassis.
 
That was it. Have no idea why I connected it to the house ground. All better.

Update

Well I did a ground to the earth because it makes the unit safer! I need to look at other things!
 
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Got of these last year, completely recapped and put it aside.

Yesterday, out of the shelf to test an old Garrard TT and there was definitely distortion from left side and a tad lower volume.
No wonder as the left output has half side dead, no continuity (open) reading on one of the plate leads. I’ve even unsoldered the wire from the socket, cut it a bit shorter to eliminate the wire as the culprit and no go, open.

As per schematic, there is supposed to have 195 ohms and 185 ohms from plates to center lead and on the left side (V3) has nothing!

Which Transcendar OPT model did you bought @chrisinsc ?

Thanks,

Patrice

***… or any other Outputs that would fit, electrically speaking?
 

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There is a pair of Hammond 1608 on the auction site right now, 10w PP 8000 ohms CT?

I also have an old Concord AF-40 (rebadged Kenwood KW-40) I got free long ago with 6BM8 PP. Could the OPT’s work in the Grommes?

I also heard about Edcor GXPP10-8K…
 
analogadict said:
A 6BQ5/EL84 pp pentode amp usually has the OPT primary impedance in the 7500 to 8000 Ohms range. To determine the exact one of the original, you can test the good one from the other channel.

Output Transformer Impedance

www.radioremembered.org

Regards,
Click to expand...
Ok, let's forget the Concord: 2500 ohms (Sams schematics). As for the Grommes, they are 6000 ohms (Sams schematics too). My options are something in the 5-6K range or a rewind... Looking at the usual suspects, Edcor, Hammond...

Thanks @analog addict !
 
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Hammond 1620A, 20w, 6,600 ohms

Edcor CXPP25-6.6K

Rewinding at Heyboer or Transcendar???
 
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