M Fowler wrote:I converted a Hammond reverb amp AO-35 to a Marshall Lite IIB one loud fun amp.
I recently found an AO-35 and now am pondering best conversion options. That power transformer seems big enough to drive more than a pair of el84s. For example a pair of 7591 or even el34s. Would require punching a second hole for an octal and using SS rectification.
Did you consider other options before doing your's up as a Marshall Lite? Any thoughts and/or advice to fuel my pondering?
I first was going to build a Dr Z Carmen Ghia but since I had already built one of those clone style new chassis, etc. I decided to go simple the IIB was it.
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I stripped the original AO-35 board and used that IIB board layout to stuff the AO-35 board and back in it went with other mods. New 40/20/20/20 JJ can cap, new tube sockets mine were not cleaning up to reuse, fuse, switches and volume/tone.
M Fowler wrote:I first was going to build a Dr Z Carmen Ghia but since I had already built one of those clone style new chassis, etc. I decided to go simple the IIB was it.
OK, thanks. Mine came through to me from an old ham and it's original working form with a new AC cord he attached. I need to pull it down off the shelf and look carefully at the both the options you've pointed at plus other potentials.
Very cool Mark. I don't see a step-down on the PT....what was the voltage output for this build off the secondaries? Looks like 2 el84 and a GZ rectifier?
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Be sure your tinfoil hat has a good low impedance ground.
donzoid wrote:Very cool Mark. I don't see a step-down on the PT....what was the voltage output for this build off the secondaries? Looks like 2 el84 and a GZ rectifier?
I tried different rectifier tubes and photo does probably have a GZ34 in but I currently run 5Y3 recto to keep things not so wild.
See ebay photo to show how it looked when I received the amp.
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M Fowler wrote:I first was going to build a Dr Z Carmen Ghia but since I had already built one of those clone style new chassis, etc. I decided to go simple the IIB was it.
OK, thanks. Mine came through to me from an old ham and it's original working form with a new AC cord he attached. I need to pull it down off the shelf and look carefully at the both the options you've pointed at plus other potentials.
AO-35 conversions into BN Lite II b 18 watt + other misc. stuf on my FB page pics. These conversions rock! You can have plenty of head room or crunch. Swap out V1 12ax7 to a 12au7 for more clean head room if needed. I gut the entire amp except for the iron and sockets. Hand built boards and new wires. This thread has got me fired up to get off my ass and build some amps again. I still have 5 or 6 of these things piled up in my shop waiting on me. My wife says thank you. btw, the schem and layout is easy to find if not just hit me up and I can email it to you. I have done so many of these that I made a sheet metal template for drilling the boards for the eyelets. 1 more thing and people may not like this but I have never run across a bad PS E cap (can cap) on these. I always check them for leakage and ESR I leave them in place also. Warm them up with a variac to reform them and they run like champs.
Hi Patrick,
I am going to assume from the Hammond schemos I have looked at (almost all of them) that your PT values are around 305 to 315 ac on the secondary. Most of them fall right into that range, with between 140 and 160mA.
I went to your FB page...impressive work! Love the wood faceplates too.
I see you are using a 150ohm block resistor. Is that to throttle your B+ voltage down a bit and if so, have you tried (for example) the Zener method. I'm certain there is a cost difference (the resistor is cheaper) but curious if there was any diff. if you had tried it.
https://www.facebook.com/trialbyfirerocks
Be sure your tinfoil hat has a good low impedance ground.
Yeah Tom, you'd have to have some pretty small hands to fit into that chassis....they are small and they are all crammed like that!
I like the way they just left that big cap can floating inside there. But after moving a few of them lately, I can see where the thing is NOT going to get jostled around much. These organs are heeaaaavy...Once they are set down in place, my guess is most of them didn't move more than once or twice in 30 or 40 years.
https://www.facebook.com/trialbyfirerocks
Be sure your tinfoil hat has a good low impedance ground.
didit wrote:
I recently found an AO-35 and now am pondering best conversion options. That power transformer seems big enough to drive more than a pair of el84s. For example a pair of 7591 or even el34s.
I recall seeing a post by someone on one of the amp boards a few years ago who indicated that he'd worked with Hammond organ trannies a lot, and that the AO35 PT, despite how big it looks on that small chassis, is not actually over-spec'd for 2xEL84. Sorry I can't give you more specifics than that, but you might want to research it before trying to use one with bigger tubes.
didit wrote:
I recently found an AO-35 and now am pondering best conversion options. That power transformer seems big enough to drive more than a pair of el84s. For example a pair of 7591 or even el34s.
I recall seeing a post by someone on one of the amp boards a few years ago who indicated that he'd worked with Hammond organ trannies a lot, and that the AO35 PT, despite how big it looks on that small chassis, is not actually over-spec'd for 2xEL84. Sorry I can't give you more specifics than that, but you might want to research it before trying to use one with bigger tubes.
I will do that. Thanks.
(edited) And I found this thread with comments from skyboltone suggesting at least to me one could swap for higher power output tubes; but upgrading the output transformer also. And also suggesting that to tamper with one is maybe murder?
donzoid wrote:Hi Patrick,
I am going to assume from the Hammond schemos I have looked at (almost all of them) that your PT values are around 305 to 315 ac on the secondary. Most of them fall right into that range, with between 140 and 160mA.
I went to your FB page...impressive work! Love the wood faceplates too.
I see you are using a 150ohm block resistor. Is that to throttle your B+ voltage down a bit and if so, have you tried (for example) the Zener method. I'm certain there is a cost difference (the resistor is cheaper) but curious if there was any diff. if you had tried it.
Thank you for the compliments and yes, right around 300v. The 150 resistor is the cathode resistor. I have never bothered to check any voltages in the circuit but I probably should. I will on my next build.
