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 Post subject: Help designing 6sj7/6sn7 input stage for 6v6 PP amplifier
PostPosted: Apr Sun 18, 2021 9:59 am 
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Joined: May Sat 25, 2019 9:42 pm
Posts: 266
Location: Royal oak MI
Hello everyone! As the title implies, I'm looking for some help designing/copying a good 6sj7 input stage for an amplifier I'm working on! This amplifier was built around the late '50s I believe! It's a nice amp, it uses ceramic sockets and stancor iron!

Anyway, I've been having some trouble with the bass clipping! This amp was originally designed to work with both a microphone and a phono input, but I gutted the front end and redesigned it for a line level input. However I'm still having some trouble with clipping... I know that the 6n7 phase inverter works just fine and I want to keep the back end of the circuit!

This amp doesn't use negative feedback or anything like that so I know I'm good as far as that goes! And I have verified that the 6n7 phase splitter works fine as the original circuit used the 6sj7 for a phono stage preamp and the mic input went through a 270k resistor into one triode of the 6n7, while the same triode also had another 270k resistor connected to the 6sj7 phono stage

I was just looking for a good circuit to use for the 6sj7 tube! I also have a 6sn7 as well! Being a push pull 6v6 amp, B+ is around 250-75v. It's a really nice amp, eventually I'm going to rebuild it onto another chassis and make her all purdy, so for the time being I'm using the old chassis as a "breadboard"...

Also I know I'm being very needy today, but I also want to design a Bass and Treble circuit, it can use 1 or 2 pots! This amp originally had three 500K pots and I took them apart and used some deoxit conductive plastics restorer and it did wonders for the pots, now they work very well!!

As always, thank you guys I always come here because you guys are the best whenever I've ever had questions, you guys always lead me into the right direction! I hope everyone has been having a great weekend! Thanks again!
Michiganamps!


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 Post subject: Re: Help designing 6sj7/6sn7 input stage for 6v6 PP amplifie
PostPosted: Apr Sun 18, 2021 11:13 pm 
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Joined: Jun Tue 17, 2008 4:52 am
Posts: 587
Location: Virginia
https://www.tdpri.com/attachments/baxan ... ng.647287/

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 Post subject: Re: Help designing 6sj7/6sn7 input stage for 6v6 PP amplifie
PostPosted: Apr Sun 18, 2021 11:23 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: 13 Critchley Avenue, PO Box 36, Monteith Ont, P0K 1P0
download/file.php?id=349630&mode=view


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 Post subject: Re: Help designing 6sj7/6sn7 input stage for 6v6 PP amplifie
PostPosted: Apr Fri 30, 2021 6:01 am 
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Joined: May Sat 25, 2019 9:42 pm
Posts: 266
Location: Royal oak MI
jukeboxman wrote:
https://www.tdpri.com/attachments/baxandall_tone_stack_layout-png.647287/


Question, I know this is an old post, I read this and thought I wrote a comment back but just realized I had not... With this type of circuit, should I add a boost circuit using maybe a triode of a 12**7 or 6**7 tube?With my amp I have a 6sj7 preamp tube driving into a 6n7 phase splitter tube, should I put this tone circuit on the signal after it's boosted by the preamp tube? I'm just worried about signal loss affecting the volume and possibly gain... , or am I worrying about nothing and it would be fine? Thanks,
John
p.s. I do like the passive components route!


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 Post subject: Re: Help designing 6sj7/6sn7 input stage for 6v6 PP amplifie
PostPosted: May Sat 01, 2021 1:50 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 27508
Location: Detroit, MI USA
Put it after the preamp.

A Baxandall tone control gives excellent boost and cut for both bass and treble, there is a minor insertion loss, but might not be enough to require any additional amplification. You can easily determine if it's good in your design without adding another stage, and if you did it would only need to be a low gain like a 6J5, 6C4, 1/2 of a 12AU7 or the like.

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Experience is what you gain when the results aren't what you were expecting.


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