I finally have gotten around to my newest project a hammond AO-43 power amp (1x12bh7,2x12ax7, 2xel84, 5u4 rect) I have done a bit of reading on these forums and have not quite found the info I have been looking for. This amp has speaker outs, reverb in/out's, gain pot, I have the gibbs reverb tank for it as well. I took it from a weathered and put out to the curb L-102 Hammond. There are of course no tone controls or volume pot, nor is there an input for a 1/4 style jack.
I am interested in the conversion if anyone has any info I would be more than glad to give further information. I have done alot of reading on tube circuits, I can solder ( I made a jimmy page push pull circuit with four push pulls in my guitar) I would like some guidance on a project like this because apparently tube amps can kill you... there is a link with perfect pictures of the exact amp as mine @ http://www.retroaudiolab.com/l102.htm, my chassis is as clean as this one if not cleaner.
Thanks!
I am interested in the conversion if anyone has any info I would be more than glad to give further information. I have done alot of reading on tube circuits, I can solder ( I made a jimmy page push pull circuit with four push pulls in my guitar) I would like some guidance on a project like this because apparently tube amps can kill you... there is a link with perfect pictures of the exact amp as mine @ http://www.retroaudiolab.com/l102.htm, my chassis is as clean as this one if not cleaner.
Thanks!
I have a similar "tone control" unit.....not sure of the make off hand. But it does use the el84s in pp........
my plan was to keep the iron(trannies, both power and output), the sockets, and then go from there with a "proven" design and build from scratch......
ive since had a different project fall into my lap, so this has taken back burner, but.....since the "new" project is now complete......this is next on the list......unless i can find a power tranny for a knight kn530(just for the amp section)......
good luck, and keep us posted on your progess....
nate
my plan was to keep the iron(trannies, both power and output), the sockets, and then go from there with a "proven" design and build from scratch......
ive since had a different project fall into my lap, so this has taken back burner, but.....since the "new" project is now complete......this is next on the list......unless i can find a power tranny for a knight kn530(just for the amp section)......
good luck, and keep us posted on your progess....
nate
Old Organ Amps
Hi,
I used to be a service tech for Hammonds ( back in the 1960's ) so I'm familiar with the overall layout of the model L amp you've got.
Because it was intended to handle the full audio range from the organ it's at least as good as any of the hi-fi amps of the period, and probably a whole lot better than the typical guitar amps.
That said, it's still only a 15 watter, so it's not really going to be useful for anything more than a practice amp.
It's a shame you junked the rest of the organ, because the original factory-fitted speakers were made by Jensen and were very efficient - 101dB per watt or thereabouts - which made the overall volume greater and covered up the smallness of the amp.
If you really want to proceed, work out where the phase-splitter stage is and feed it with a line-level signal - remove or disconnect all the earlier stages as they have frequency compensation round them to make the volume pedal of the organ work like a 'loudness' control.
The reverb tank is driven by the 12BH7 stage and the output was controlled by some switches you no longer have, so I'd suggest you forget reverb for now...
I've probably still got schematics for the L series - I'll have a look in the loft.
The best one to play with would be the PR-40 tone cabinet amp - it had three channels - two like the one you've got and one with four output tubes for the bass. The box had a 15" bass driver and a pair of 12" - one in the front and the other in the top...
While we're on the subject of old tube amps, the ones in the Leslie speakers were also very good - they used a pair of 6550's and produced a solid 50 Watts. Leslie made a pre-amp so you could plug a guitar straight in...
Graham.
Hi,
I used to be a service tech for Hammonds ( back in the 1960's ) so I'm familiar with the overall layout of the model L amp you've got.
Because it was intended to handle the full audio range from the organ it's at least as good as any of the hi-fi amps of the period, and probably a whole lot better than the typical guitar amps.
That said, it's still only a 15 watter, so it's not really going to be useful for anything more than a practice amp.
It's a shame you junked the rest of the organ, because the original factory-fitted speakers were made by Jensen and were very efficient - 101dB per watt or thereabouts - which made the overall volume greater and covered up the smallness of the amp.
If you really want to proceed, work out where the phase-splitter stage is and feed it with a line-level signal - remove or disconnect all the earlier stages as they have frequency compensation round them to make the volume pedal of the organ work like a 'loudness' control.
The reverb tank is driven by the 12BH7 stage and the output was controlled by some switches you no longer have, so I'd suggest you forget reverb for now...
I've probably still got schematics for the L series - I'll have a look in the loft.
The best one to play with would be the PR-40 tone cabinet amp - it had three channels - two like the one you've got and one with four output tubes for the bass. The box had a 15" bass driver and a pair of 12" - one in the front and the other in the top...
While we're on the subject of old tube amps, the ones in the Leslie speakers were also very good - they used a pair of 6550's and produced a solid 50 Watts. Leslie made a pre-amp so you could plug a guitar straight in...
Graham.
Graham,
I have an AO-35 in it's own stand alone cabinet. I was told by Capt. Foldback (http://www.captain-foldback.com/) that this is a prime candidate for conversion to guitar amp. Again, low power, but could be great for an acoustic/blues amp in the LR.
Any input there? Schematics for a number of Hammond equipment can be found on Capt. Foldback's site.
I have an AO-35 in it's own stand alone cabinet. I was told by Capt. Foldback (http://www.captain-foldback.com/) that this is a prime candidate for conversion to guitar amp. Again, low power, but could be great for an acoustic/blues amp in the LR.
Any input there? Schematics for a number of Hammond equipment can be found on Capt. Foldback's site.
Old Organ Amps
Hi again,
I've got a boxful of old organ manuals in the loft, but without knowing which model the chassis you refer to came from, I've got no idea where to start.
The units sold in the UK often had different reference codes to the US stuff - mostly because of the different mains voltage, but also because the franchisees here were independant and often specified variations of the standard product in the belief that they would sell better. Certainly all the cabinets were made over here ( to save on shipping ), so the styles are different.
I'll do anything I can to help, but it may take a little time to locate the information.
All the best, Graham.
Hi again,
I've got a boxful of old organ manuals in the loft, but without knowing which model the chassis you refer to came from, I've got no idea where to start.
The units sold in the UK often had different reference codes to the US stuff - mostly because of the different mains voltage, but also because the franchisees here were independant and often specified variations of the standard product in the belief that they would sell better. Certainly all the cabinets were made over here ( to save on shipping ), so the styles are different.
I'll do anything I can to help, but it may take a little time to locate the information.
All the best, Graham.
Hammond Conversion AMP - Goodsell Amps
Goodsell Amps in Atlanta started as Hammond conversion from A100 and others. Richards amps today are very demanded and unbelievable based on his experience as a Hammond tech and his reverse engineering of the older Hammond tube amps.
If you heard them you would understand the desire to build one. At 17 watts the conversion are so unbelievable it can be described. Look around at the comments on the web.
Link to Atlanta Discount Music for his amps
http://www.atlantadiscountmusic.com/goodsell.aspx
Goodsell Amps in Atlanta started as Hammond conversion from A100 and others. Richards amps today are very demanded and unbelievable based on his experience as a Hammond tech and his reverse engineering of the older Hammond tube amps.
If you heard them you would understand the desire to build one. At 17 watts the conversion are so unbelievable it can be described. Look around at the comments on the web.
Link to Atlanta Discount Music for his amps
http://www.atlantadiscountmusic.com/goodsell.aspx
Hammond amp mods
From the circuit I'd guess you have way too much gain - you're probably over-driving the second stage with a guitar signal and a gain of 600+. After that, there's no way back.
The reverb spring output was about 2mV and a guitar is at least 200...
I'd add a volume control where you've reduced the resistor value to 220K - it will need a series cap to block the DC on the grid of the phase-splitter stage.
At least that will let you listen to what's being over-driven in the input stages.
From the circuit I'd guess you have way too much gain - you're probably over-driving the second stage with a guitar signal and a gain of 600+. After that, there's no way back.
The reverb spring output was about 2mV and a guitar is at least 200...
I'd add a volume control where you've reduced the resistor value to 220K - it will need a series cap to block the DC on the grid of the phase-splitter stage.
At least that will let you listen to what's being over-driven in the input stages.
According to the schematic, I see no problem making a conversion for guitar.
You'll need to replace most of the resistors and caps, lose a few, add a few, but the tubes and transformers are probably ideal as is.
I would lose the feeback circuit from the output altogether.... but not UNTIL you reduce the gain of that second stage!!!
Check out AX84.com and look at their High Octane guitar amp project. I would modify your preamp stages to model the High Octane. It's a winner. High Octane Schematic
Or... you could opt for their S.E.L. model, known as the Single Ended Lead project, which has a little more crunch and grunge. (but your power tranformer is probably better suited for the H.O., since your schematic indicates 300v on the output stage.)
The H.O. and the S.E.L. are both "single ended" output models, and your's is push-pull, but your preamp stages should be all you need to modify to get her going, and you already have most of what you need.
Your hammond "pushpull output stage" looks pretty good to go as is. This should make a terrific little amp. I should be so lucky to come across junk like that!
AX84 also has some push-pull projects too if you want to compare stages. Look in the Classic Amp Projects section. You can marry just about any preamp to any ouptput stage, depending on your taste, and thurst for power.
I'd begin there... and then tweak it to suit.
You'll need to replace most of the resistors and caps, lose a few, add a few, but the tubes and transformers are probably ideal as is.
I would lose the feeback circuit from the output altogether.... but not UNTIL you reduce the gain of that second stage!!!
Check out AX84.com and look at their High Octane guitar amp project. I would modify your preamp stages to model the High Octane. It's a winner. High Octane Schematic
Or... you could opt for their S.E.L. model, known as the Single Ended Lead project, which has a little more crunch and grunge. (but your power tranformer is probably better suited for the H.O., since your schematic indicates 300v on the output stage.)
The H.O. and the S.E.L. are both "single ended" output models, and your's is push-pull, but your preamp stages should be all you need to modify to get her going, and you already have most of what you need.
Your hammond "pushpull output stage" looks pretty good to go as is. This should make a terrific little amp. I should be so lucky to come across junk like that!
AX84 also has some push-pull projects too if you want to compare stages. Look in the Classic Amp Projects section. You can marry just about any preamp to any ouptput stage, depending on your taste, and thurst for power.
I'd begin there... and then tweak it to suit.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.