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Hoffman Amps Forum image Author Topic: Will this work?  (Read 2283 times)

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Offline Stuff4bikes

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Will this work?
« on: April 18, 2022, 08:34:11 pm »
PP 6v6gt amp
5u4gb rectifier
6sc7 PI using half for the pre amp and half PI.
Channel 1 6sf5gt
Channel 2 6sj7.

Each channel will have seperate inputs, vol and tone controls.
I have 4 sj's  to find a quiet one, if not I will try sg's I have a half dozen.
I can use sn7's if the PI doesn't work out.....

Any schematics with this similar tube line up..?


Offline sluckey

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Re: Will this work?
« Reply #1 on: April 18, 2022, 09:05:39 pm »
Quote
6sc7 PI using half for the pre amp and half PI.
This tube has cathodes internally connected so won't work.
A schematic, layout, and hi-rez pics are very useful for troubleshooting your amp. Don't wait to be asked. JUST DO IT!

Offline Stuff4bikes

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Re: Will this work?
« Reply #2 on: April 18, 2022, 09:12:36 pm »
 can I parralel the two sides of the 6sc7 and run it at V1 and use the 6sf5 as the PI?
Man I have a bunch of questions but not sure they make sense.


Offline Molwam

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Re: Will this work?
« Reply #3 on: April 19, 2022, 03:26:52 am »
You could use the 6sc7 as a LTP phase inverter. Even its data sheet states that is was designed to be a phase inverter (https://frank.pocnet.net/sheets/201/6/6SC7.pdf).

Offline Stuff4bikes

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Re: Will this work?
« Reply #4 on: April 19, 2022, 08:18:23 am »
I have decided not to use the 6sc7 for this build.....pretty sure I am going to need another gain stage on one or both
Channels before the PI.

Offline bmccowan

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Re: Will this work?
« Reply #5 on: April 19, 2022, 12:13:13 pm »
Quote
Any schematics with this similar tube line up..?
PP 6v6gt amp
5u4gb rectifier
6sc7 PI using half for the pre amp and half PI.
Channel 1 6sf5gt
Channel 2 6sj7.
Sure - there are many amps that use those tubes. Although an exception is the 6sf5, but I think that is basically equivalent to 1/2 of a 12AX7. Many, many all octal amps from the 40s and 50s used the 6sj7 as the V1 and some that used multiples. It often is followed by a 6N7, 6SN7, 6SL7, 6SC7, or additional 6SJ7s. I have a cool Danelectro that has 3 6SJ7s and 2x6v6. If you look through Valco, Gibson, Rickenbacher, Dan Electro, Flot-a-tone, etc. schematics from that era you will find many examples. What flavor are you looking to build?
Mac
“To my surprise, when I opened my eyes, I was the victim of a great compromise.”
John Prine

Offline Stuff4bikes

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Re: Will this work?
« Reply #6 on: April 20, 2022, 12:03:40 am »
Well the experiment has progressed.....

6sg7......the 6sj7's just screamed with any kind of volume.....
Into a 6sf5gt feeding a parallel set of 6v6gt's....
I only have about 265v on the plates of the 6v6's but just a small sound check seemed promising.....

I don't play guitar very well but my friend who is strictly a Marshall guy enjoys my creations.....many times
I will just make something and then he plays through it and then I disassemble it and start something else.
I just enjoy tinkering with electronics, it mirrors my job----except no tube equipment at work.

Offline bmccowan

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Re: Will this work?
« Reply #7 on: April 20, 2022, 06:51:57 am »
Quote
the 6sj7's just screamed with any kind of volume
I assume you are using "screamed" as a negative term. You said that you had 4 of them to try. Unless they were all old pulls, I would suggest that you might not have had things set up right for that tube. Anyways keep us posted. BTW, the early Gibsonette and GA-9 amps are 6SJ7 feeding parallel 6V6s - no additional gain tube. Plate voltage in those amps is only slightly higher than what you have.
Mac
“To my surprise, when I opened my eyes, I was the victim of a great compromise.”
John Prine

Offline Stuff4bikes

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Re: Will this work?
« Reply #8 on: April 20, 2022, 08:17:18 am »
Sorry, screamed in a bad way. Honestly the 6sg7's seemed to work well...further testing will surely be needed...
First two sj's were noisy. Put in an sg7 and no noise so let's give it a shot..I may revisit the sj's, I think I have some more from a hammond pull.

####    looking at the Gibson ga 9 schematic you mentioned, my voltages are a little higher at V1 than gibsons.....maybe that's why I had problems with the sj7's.
« Last Edit: April 20, 2022, 08:38:42 am by Stuff4bikes »

 


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