Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Rontone on February 16, 2023, 07:51:48 pm
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I got a pile of Hammond stuff as I wanted to do some American amps,
Got A0-63 and AO-43 amps, 7x Preamps and 4x Gibbs Spring Reverbs, a few Vibrato scanners and line box, and so many preamp tubes from the 7 preamps :icon_biggrin:
Sluckey's AO-43 and 63 conversions look excellent, so I think the big AO-63 should turn into a 6L6 beast, Fendery Dumbley thing,
The AO-43 iron can be kept together too, I'm getting around 335v on the Mains TX, 5V and 6.3v all good, the OT runs a pair of 6V6's on Sluckeys Plexi build, but can't decide on the circuit
So many choices between 1950 -1970 circuits and their slight variations, Deluxes, Princetons, early 6V6 Supers etc, I've never tried/played a 5E3 type circuit so I guess that's a rite of passage too
So an AB763 type thing is covered by the big AO-63, any recommendations on what other Fender or Gibson etc 6V6 P-P circuits have an 'alternative' sound, different tone-stacks or phase inverters etc to widen the range of sounds between these builds, maybe one from the 50's and one from the 60's for the remaining two?
There's so many sounds its all very subjective I know, theres Neil Youngs old tweed farts, theres the Eagles golden crunch, Albert Collins's icepick to the forehead,
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Options that are not Fendery for the 43 are huge. Many cathode biased Gibson and Valco amps to consider. For Gibsons, the GA-20/30/40 amps that have 5879 preamps are very cool. The GA-16T is another favorite. Nearly any of the Valco 50s & 60s preamps can be used with either 6V6s or 6973s.
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So an AB763 type thing is covered by the big AO-63
I left the PI and power amp original and just added an Ampeg preamp with James Tone Stack. Powerful, clean, warm sound. Not Fendery at all.
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Options that are not Fendery for the 43 are huge. Many cathode biased Gibson and Valco amps to consider. For Gibsons, the GA-20/30/40 amps that have 5879 preamps are very cool. The GA-16T is another favorite. Nearly any of the Valco 50s & 60s preamps can be used with either 6V6s or 6973s.
The 43 would make a great Gibson type, it already has 6BQ5, 12AX7 and 12BH7 engraved on the chassis for the tubes, would be good to pick one of those PP 6BQ5 type circuits, keep these chassis engravings, there's is also a 12BH7 on there, so there's a way to keep it on there as with the Hammond its for the reverb so might as well use it,
I will keep staring at Gibson/Epiphone schematics, I need to learn more about Valcos
I left the PI and power amp original and just added an Ampeg preamp with James Tone Stack. Powerful, clean, warm sound. Not Fendery at all.
Yeah, I was thinking of converting that just like yours, keep the Gemini with James tone-stack, but add another preamp channel, just join with mixing resistors as I have seen with other amps, I don't mind using an A-B box pedal to switch between channels,
One thing I noticed was where you had your reverb send hooked from in your Gemini preamp, you said you had found just the right spot after some experimentation, before the tone-stack, but if I added another channel and mixing resistors it would limit me to adding the reverb send after those mixer resistors to get reverb on both channels,
So don't know if that's ok, or if values of those resistors/caps at the reverb input need changing to account for a change in impedance maybe? When you tried it post tone-stack was it loading the reverb differently, draggin it down?
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When you tried it post tone-stack was it loading the reverb differently, draggin it down?
It's been over 7 years. I don't remember. All I can say is it sounds good when wired IAW my schematic. :icon_biggrin:
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The 43 would make a great Gibson type, it already has 6BQ5, 12AX7 and 12BH7 engraved on the chassis for the tubes, would be good to pick one of those PP 6BQ5 type circuits, keep these chassis engravings, there's is also a 12BH7 on there, so there's a way to keep it on there as with the Hammond its for the reverb so might as well use it,
I will keep staring at Gibson/Epiphone schematics, I need to learn more about Valcos
The Gibsons I was referring to are mostly 6V6 amps - but any of those preamps could be adapted to 6BQ5 use. Gibson did produce some 6BQ5 amps with mixed results - some have some unusual "T-filters" that were added to the preamp circuits, supposedly to clean up the sound. The filters are easily designed out.
Valco also did not do many 6BQ5 amps, but the 6973 amps can be easily be done with 6BQ5 power tubes. One 6BQ5 Valco I want to build some day is the Harmony 415. Ken Fisher raved about that amp. The 43 would be a good donor for that circuit.
And I get the chassis has the tube types engraved thing. I have the same thing with a current project. A Knight mono Hi-Fi chassis that has 5Y3, 2x6V6, 6SL7, 2x6SN7 printed on the chassis, so I am sticking with that and using Sluckey's Rocky and Ampeg circuits as starting points.
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One 6BQ5 Valco I want to build some day is the Harmony 415. Ken Fisher raved about that amp. The 43 would be a good donor for that circuit.
Yes, that is the one, this means I will have to get 2 x 12" C12 Jensens for it :icon_biggrin:
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Coming in late here, but you can make a very strong AB763 DR out of the AO-43 transformers. The choke is 15H and works well also. I'm happy with running 6V6s in it but I honestly think it might handle 6L6s too. Anyway, I built the bias that way in case I ever get crazy and decide I must have a Pro Reverb.
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Coming in late here, but you can make a very strong AB763 DR out of the AO-43 transformers. The choke is 15H and works well also. I'm happy with running 6V6s in it but I honestly think it might handle 6L6s too. Anyway, I built the bias that way in case I ever get crazy and decide I must have a Pro Reverb.
Maybe a cathode biased 6v6 for the AO-43, just cut out the 9 pin sockets and add a piece of chassis for the 6v6 sockets. You can clean the cone bd and use it, just move over to center making room for pots. I used that cone bd for a 6v6 plexi, a little stuffed in but sounded great.
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I used a Princeton chassis and cabinet. I could not get that cone board clean no matter what I did. Propane torch just melted the board before it melted solder.
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...you can make a very strong AB763 DR out of the AO-43 transformers. The choke is 15H and works well also.
I think the AO-43 is going to turn into a Harmony, keeping the mains and OT together, the Harmony 415 schematic doesn't require the choke, so that choke, and the remaining small O/T from the AO-63's reverb output section can be used on the third amp, with a new mains transformer, and it will be 6V6 of some kind!
Maybe a cathode biased 6v6 for the AO-43, just cut out the 9 pin sockets and add a piece of chassis for the 6v6 sockets.
I'm thinking a nice fresh chassis for the 3rd one for that very reason to do a octal socket beast,
I used a Princeton chassis and cabinet. I could not get that cone board clean no matter what I did. Propane torch just melted the board before it melted solder.
Yeah, its tough that stuff, I pulled a bit too hard on one component and it pulled the eyelet/cone a bit, cracking along it to the edge, its not too bad and will work again, but I think I will save it for an emergency, or build an FX pedal with it etc,
So this should build me 3 nice amps, a huge 2x 6L6 AO-63 beast, an A0-43 into a 'Ham-rony 420 special'
Then its this 6V6 one left to narrow down and mull over, I think I will have an AB763 channel already, so it might have to turn into a good old 5E3 tweed monster, there are brand new power transformers that look the part available, black Hammond/Fender style looks to match the OT and choke