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Has anyone ever worked on this or a similar topology amp? With a 6L6GC driving a tranformer into an output stage with 6 special selected TS 6550's?
Thanks!
Follow Ups:
I bought the transformers form Bob Rissi off eBay. Heavy man.
The 6L6 into Interstage is the balls. I was using crappy tubes in the testing phase shown above. Here also, I am using a 6V6GT as the interstage driver. 6SL7s as preamp tubes because I like octals. It is one amp I would like back, but is is being used by a touring band. I bought a bunch of Bob's interstage transformers. I have a new PS300 OPT as well.
Edits: 04/20/12
So for you the 6v6 is enough to drive the Interstage yes...
I do like the 6v6 in triode just bit better than 6l6, so cool amp...
wow! Fender also uses a bit of feedback just around the front end, so this is partly why it is quieter than you thought....I think effective, because it probably solidifies the deep bass a bit also...
So FenderLover is this going to be your next build...hehe???
Just when I thought Ampeg was King....mmmm hehe
Have Fun, thanks, and Good Music to you,
-3db
Very cool! You go through the 30-step (or whatever it is) adjustment of idle bias, as the 400PS?
Bet a Precision would sound heavenly on your amp! Would love to have been able to try one out.
Once you set it up, it is really stable. It runs "deep" class B so changing the output tubes requires nothing. I did not do the extensive graphic equalizer section of the amp.When I first fired it up, I thought I did something terribly wrong. I got nothing, zilch, out of the speakers at idle. I thought that with 700 volts coursing through the thing, tracking down noise would be an issue. Frustrated, I plugged a guitar in anyway and about deafened myself. Man is that thing was quiet at idle. It was so powerful that there was no way for me to test it at the upper end with my speakers without destroying them, cool.
It is nice having digital photos of old amps, they really bring back the experience of building and owning the piece.
After this amp, it was clear to me that the magic of an amp lies in its driver circuit. Since then I have overbuilt my output stage drivers and never looked back.
Edits: 04/20/12 04/20/12
And I'm not so wonderful at bass. 8^)
You made one of the best DIY ever. But, to find those trannies, today. I supposed one could have them specially wound. But, I bet the standards used by Schumacher and others, at the time was pretty darn high. Much higher than the average high powered amp OPT's of today.
You get 300 watts or more off your amp? And did you run JBL K130's? I LOVED those and the K120's. Loudest, best sounding speakers.
Boy, sextet of GE 6550A at today's prices?
I've serviced a few. They are rare.
It's an unusual circuit. The OT has three secondary windings, each with it's own output jack. They are switching jacks. Each switching jack completes the cathode connection of two power tubes when you plug in.
With only one jack in use, two power tubes are functional. With two cabinets connected, four tubes are functional. With three cabinets, all six 6550's are working.
Fender also made a 300PS, with four 6550's, but I've never seen one.
The Tung-Sols were supplanted by GE 6550As in fairly short order. Check the link below for some interesting stuff!
Edited to fix typo...
Edits: 04/22/12
Yeah, great site. I have it in my bookmarks.
Curious though about monitoring the AC lone current to set bias. Apparently they claim it's the official set up procedure.
Anyone know more about it?
There really is no "they" - it's Rich Koerner, the owner/operator of Time Electronics.
If you look at his updates and modifications page you can see the procedure. It's credited to Ed Jahns (Fender) and dated in the 1970 range.
I know Rich personally - and while he is definitely a "curmudgeon", he also knows his stuff BIG time. I have no doubt about the authenticity of what he has up on the site.
One of the pics on the site shows Rich a NUMBER of years ago with his black cowboy hat on while working on a 400-PS. He's been around these things from the get-go.
That is an interesting point. I haven't seen one of these measuring instruments in any amp tech's collection. Maybe, it's from AM and SSB transmitter tech stash of goodies.
I would love to take a look at the guts of that beast! Man, those absolutely MELTED 6550's! Amazing.
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