Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: glassesnvests on January 30, 2015, 09:22:15 am
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So I found a schematic for the Divided by 13 CJ11 on the webs, and am wanting to give it a shot..
Really it's not that complicated of an amp, just an AB763 Deluxe preamp biased a little glassywith 3k3 cathode resistors into a 5e3ish PI and power section.
My goal is to make it more complicated and to try and make it to where the amp can take el34's, 6L6's and 6V6's. I've searched a ton online and haven't found anything definitive.
I was thinking of using these transformers,
Hammond 1645 https://www.tubesandmore.com/products/P-T1645 (https://www.tubesandmore.com/products/P-T1645)
Hammond Deluxe reverb PT https://www.tubesandmore.com/products/P-TF41316 (https://www.tubesandmore.com/products/P-TF41316)
Thoughts? My thinking for using the DR PT was so I could have ample current rating for the power section, and I'll be using the GZ34.
All input appreciated! Thanks!
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If you want to use EL34 tubes then you need PT with more heater current because one EL34 takes 1,5A.
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The EL34 tubes have 11mA/V sensibility, the 6L6 6mA/V, the 6V6 4.1mA/V
so, you must consider also that if the original has a PI planned to drive low Siemens tubes like the 6V6, inserting 6L6 and more, the EL36
will give you less headroom (may be you want this thing), you can tame this effect using the LarMar PPIMV that is present on your schematic
about it, I don't see the utility of the two 2.2M resistor connected between the wiper of the pot and ground, this amp is cathode biased and
a fault on the wiper connection of the MV pot didn't represent a big trouble (no bias loss like if the amp was fixed bias) only a mute effect
on the branch of the PP with the wiper disconnected, a fake SE effect
if you want, you can reach this inserting a switch to connect to ground one of the final tubes grid, disconnecting it from the signal
As to use different tubes of course you need enough current on the PT, I mean filament current and, if you want the max power that the tubes
can give, you must also have an adequate B+ current to satisfy the request + an adequate OT
Of course you must adjust bias using a switch and an adequate value resistor to be put in parallel with the "standard" cathode resistor
considering as standard the resistor that is adequate to the tube that needs the higher cathode resistor value
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On this tread you can see a hand draw schematic that is without the PPIMV
http://el34world.com/Forum/index.php?topic=15506.msg149574#msg149574 (http://el34world.com/Forum/index.php?topic=15506.msg149574#msg149574)
K
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So say I like the PT that I found, (cost, size) what if I just used an external filament supply? AES has ones rated for 4 or 6 amps for under $20. Assuming I throw in some el34's, and throw the altered bias resistor switch, all other things should be fine with just some tweaking to taste?