Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: rsr on December 29, 2018, 01:35:46 pm
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I built a blues junior conversion amp last year, and it is working fine.
Re-used the stock PT and a heyboer TO20B output transformer, but everything else was according to the hoffman diagram.
Recently, i picked up an Allen TP24 transformer for next to nothing and am wondering if it would be worth putting that into the BJR.
Not going to change from EL84 tubes or anything like that, but am wondering if this PT would be any quieter. I would also enjoy a little more clean headroom if it brings that to the party.
Anyway, on the Allen website it says this
Allen transformers are perfect for repairs and replacements of most of the more popular vintage Fender™ amplifiers or for your own custom-built projects. Period correct voltages and equal or better current ratings. Direct bolt-in replacements with no drilling necessary. Improved features such as Unistrand pre-tinned wiring for easy soldering, center-tapped heater windings on power transformers for convenient grounding (without the need for 100 ohm grounding resistors at the pilot light) and internal hum shield brought out to a lead for grounding power transformers to reduce hum emissions.
My question is whether there are any changes to the circuit that should be made if using this PT. Like, should i eliminate the resistors on the tube board between the filaments and ground, as that seems to be what is suggested above?
Any other thoughts or advice always appreciated.
roger
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If you use the filament CT ya don't need the R's, clean headroom Is the amount of swing your signal has before it runs into the "stops", assuming the signal is clean to begin with. so If B+ didn't go up, or bias change ya get what you had
quiet is primarily low noise to signal, so unless you get lucky and lay the wires "better"......
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Maybe off topic - why did Hoffman use 47 ohm resistors for the artificial center tap instead of 100 ohms? Was it because or the PT filament winding used?
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> why did Hoffman use 47 ohm
Maybe he had a lot of them?
I once used 68 for *everything* because a load fell from a truck, literally. When I needed hi-power 1K, I nailed like 15 of them on the side wall of the cabinet.
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PRR said "I once used 68 for *everything* because a load fell from a truck, literally. When I needed hi-power 1K, I nailed like 15 of them on the side wall of the cabinet. "
:l2:
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I spent 20yrs climbing in east Ky, made friends with some locals that always seemed to have;
a load fell from a truck
, I had extra back then and they didn't, no R's but lots of broke slot machines :icon_biggrin: