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building a tube amp with assorted tubes
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Author:  nkiki2000 [ 09 Oct 2019, 16:54 ]
Post subject:  building a tube amp with assorted tubes

I have recently had these tubes come into my possession: 6be6 6ba6 6AQ5A 6AV6
Im looking to build a tube amplifier with these tubes but i do not know where to start.

Author:  mike567 [ 14 Oct 2019, 18:41 ]
Post subject:  Re: building a tube amp with assorted tubes

find a copy of an AA5 radio and copy the output section using the 6av6 driving the 6aq5. Use a regular power transformer . do not connect the tubes directly to the line.

Author:  ILoveHiFi [ 15 Oct 2019, 01:44 ]
Post subject:  Re: building a tube amp with assorted tubes

NOS 12ax7 12au7 and hifi sound quailty and made in USA etc and fancy brands don't cost much.
Considering you can buy like mullard and simens for like 60 - 120USD for a pair.

Author:  Trackhappy [ 15 Oct 2019, 18:42 ]
Post subject:  Re: building a tube amp with assorted tubes

Hi nkiki2000,
I have just worked up a design using 6AV6 and 6AQ5. I'll post the schematic when I get home tonight if you like. I called it Jabob (Just A Bunch Of Bits) because my Wife said I can't build anymore amplifiers.. :(
It sounds ok, but I have yet to finish playing. I specifically built it using cheap components such as Altronics M1120 transformers just to see how good I could get it.
Cheers,
Glenn.

Author:  Trackhappy [ 15 Oct 2019, 19:04 ]
Post subject:  Re: building a tube amp with assorted tubes

Found it:
Attachment:
Jabob schematic marked up[1].jpg


Hmmm, that image is a too small, will upload a bigger one tonight.

Author:  Trackhappy [ 16 Oct 2019, 03:10 ]
Post subject:  Re: building a tube amp with assorted tubes

Better picture attached.

Attachment:
Jabob schematic marked up.jpg


R15 chosen for 2mA shared between the two 6AV6's. R2 chosen to have about 30% across it, which apparently gives a good balance of the outputs. Feedback seems to do very little as it is drawn. Disconnecting gives no audible difference. I have to run a frequency sweep again to check response, but it sounds good on the crappy speakers I have. They sound " boomy", but until I get my Frugelhorns back from painting I won't really know.
6AQ5's are rated at 250V B+ but as you can see I am running them hot. I am a little worried about the screen voltages being high, tempted to regulate as they should also be 250V but they may cause excess screen dissipation and valve failure.

Anyhow, if it is of use, great. I might document the build in a build thread for anybody else on a serious budget.
Cheers,
Glenn.

Author:  nkiki2000 [ 22 Oct 2019, 07:58 ]
Post subject:  Re: building a tube amp with assorted tubes

thanks for the schematic, i think im going to give building that a shot, ill come back here when i get it done!

Author:  Trackhappy [ 22 Oct 2019, 14:40 ]
Post subject:  Re: building a tube amp with assorted tubes

I just spotted an error in my cad drawing. Don't connect pin 7 and pin 2 together.

Author:  ILoveHiFi [ 22 Oct 2019, 20:32 ]
Post subject:  Re: building a tube amp with assorted tubes

http://www.valvewizard.co.uk/pentode.html
If you don't connect pin 7 pin 2 together then it will not work

Author:  Trackhappy [ 22 Oct 2019, 21:37 ]
Post subject:  Re: building a tube amp with assorted tubes

ILoveHiFi is quite correct of course, my pins are wrong in the diagram (thats what happens when you pinch somebody else's component library).

There is definitely a mistake. Pin 1 and 7 are internally connected in a 6AQ5, which is first grid G1. Suppressor grid is internally connected to the cathode. Just leave pin 7 disconnected.

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