I agree with DF96, do that, and you can keep the current in the output transformer halves equal to prevent early saturation.
24V is a good check, and so is the 350V on the screens, and 400V on the plates,
Then check that the current times the voltage does not exceed the tube plate and screen power dissipation ratings (easier said than done, because there are no screen resistors to be able to test the screen current. I bet a 100 Ohm screen resistor to each screen would not appreciably affect the amp performance, but would allow easy testing of screen current with a DMM.
If I had that amp I would put those resistors in there.
24V is a good check, and so is the 350V on the screens, and 400V on the plates,
Then check that the current times the voltage does not exceed the tube plate and screen power dissipation ratings (easier said than done, because there are no screen resistors to be able to test the screen current. I bet a 100 Ohm screen resistor to each screen would not appreciably affect the amp performance, but would allow easy testing of screen current with a DMM.
If I had that amp I would put those resistors in there.
Thank you and JonSnell. The organ sounds incredible, but I was concerned to avoid blowing the tubes, which is why I asked the question I the first place. The bass is a little funky sounding, though. Instinctively, you folks chimed in with what is really important, and why. This is most appreciated.
I was underneath planning to replace all the carbon and noticed one resistor in the mix of this section (bass) is out of spec high.
From the little reading I've done on power tubes, it does not seem prudent to risk an open anywhere while energized, especially just to save a few bucks.
The screen resistors are going in. It is not Hi-Fi so I doubt anyone would notice any loss in sound quality. May as well get rid of all the carbon, then set the balance. All the voltages are dead on, after all the electrolytics were replaced.
This is the bass channel amplifier of a Hammond H-100 organ, isn't it? As yet mentioned above, there is no way to adjust bias really. The -24v is a fixed voltage, coming from the lowermost winding of the power xformer (see complete schematics) via the rectifying and smoothing network of D703, C704, C705, R704 and R707. Trimpot R417 serves for DC bias symmetry of both 7591 output tubes.
Best regards!
Best regards!
Monstrosity
It is indeed the bass channel, Kay. All those components were replaced with new, and there is the -24v coming out exactly. Strange way of making the negative--half-wave rectifier--but it works.
I cannot find the precise schematics for this particular version. There are some changes, but most of it is the same. For instance, resistors are used instead of inductors for smoothing the HT. Also the two preamps are solid state in lieu of tubes. Fortunately, these amps are the exact part numbers of those used in the R-100. There was also a small board (with many transistors) connected to the signal input to the audio amplifier. I read in a forum that it is some kind of suppressor, and that when it goes bad, the signal is reduced to an unusable level. The writer said if that happens to simply disconnect it. That happened to me and when it was disconnected, the volume returned. It blew/shorted around the time a contact cleaning was performed. Two days were spent trying to locate the problem.
There is a large, chassis mount diode or zener in the amplifier chassis. I have yet to determine what it is used for. The circuit must be derived by tracing all the connections visually, and hopefully finding the part specs by the identifying number.
The machine has a reputation of having curses hailed down upon it by Hammond technicians. It is significantly more complex than a B3/C3. It appears they attempted to make it all things to all people. If it were not for the extra harmonics, especially the bass, I would not have acquired it.
It is indeed the bass channel, Kay. All those components were replaced with new, and there is the -24v coming out exactly. Strange way of making the negative--half-wave rectifier--but it works.
I cannot find the precise schematics for this particular version. There are some changes, but most of it is the same. For instance, resistors are used instead of inductors for smoothing the HT. Also the two preamps are solid state in lieu of tubes. Fortunately, these amps are the exact part numbers of those used in the R-100. There was also a small board (with many transistors) connected to the signal input to the audio amplifier. I read in a forum that it is some kind of suppressor, and that when it goes bad, the signal is reduced to an unusable level. The writer said if that happens to simply disconnect it. That happened to me and when it was disconnected, the volume returned. It blew/shorted around the time a contact cleaning was performed. Two days were spent trying to locate the problem.
There is a large, chassis mount diode or zener in the amplifier chassis. I have yet to determine what it is used for. The circuit must be derived by tracing all the connections visually, and hopefully finding the part specs by the identifying number.
The machine has a reputation of having curses hailed down upon it by Hammond technicians. It is significantly more complex than a B3/C3. It appears they attempted to make it all things to all people. If it were not for the extra harmonics, especially the bass, I would not have acquired it.
Yes, the H-100 series is known of being very complex, complicated - and somewhat brittle. I would have expected that there were more harmonics in the treble region, due to it's real 96 tone generator?
And sorry for confusing R704 and R706, the service manual that I could find ist not that readable.
Best regards!
True. The bass has four drawbars instead of two, and the upper manual has an extra two, the lower manual one extra, compared with B3/C3.
Brittle? It has a 2.1 internal amplifier/speakers. The bass is "derived" from the two channels. Only two Leslie models were designed to work with it. That may explain. Also there is no guidance on utilizing the extra harmonics. Most players do not know how to set the manuals on this model anyway, and neither do I.
There is no tone control on mine. Other versions have a tone pot on the amp.
Brittle? It has a 2.1 internal amplifier/speakers. The bass is "derived" from the two channels. Only two Leslie models were designed to work with it. That may explain. Also there is no guidance on utilizing the extra harmonics. Most players do not know how to set the manuals on this model anyway, and neither do I.
There is no tone control on mine. Other versions have a tone pot on the amp.
Definitely agreed there. Solid wires from the tone generators, carbon resistors, low quality PCBs, too many signal connections. However, it is repairable, rebuildable, and could be extensively modified. Stripping or jumping some of the useless extras might be an option for some. Have to be careful here because there may be hum cancellation inherent in the spaghetti-bowl wiring, and of course in the amp.
?
Welcome to the H-100 club.
I've got three of them. None of them are up to date enough for the solid state preamps. Tubes all the way. All were working rather feebly and wimpily when I bought them 2010-2012, so I'd say reliability is not the problem.
The carbon comp resistors are not the problem, except there is a 10k in the power amp chassis that is always burned to 11.5k to 13.5 k. Look for a 10k with burned paint.
Replace with a 2 or 3 watt metal film resistor.
If the power amp cap has been particularly leaky, there is a 220 ohm resistor near the left wall that is burned. Check and replace as necessary. Only one of my 3 units needed it.
If you check them I think you'll find 99% of the carbon comp caps are in tolerance. At least if you organ was built in Chicago and they were still using mil-spec equivalent suppliers when yours was built. Mine are in spec. Units built in Holland, including the legendary X66, have mostly high value resistors by now.
The main problem, IMHO, is the electrolytic & tantalum caps. I replaced 71 of them in one unit, and the sound level tripled, the bass got much more commanding, and the trebles started to really shine when called for. With bad e-caps, even the ones up in the preamps on the back of the keyboards, the trebles are almost inaudible. I used film and a few 10 uf ceramic caps on the preamps where the film caps wouldn't fit. I did not remove the preamp boards, I just cut the axial wires, made hooks, and hooked the new caps over the old leads.
There was one pot that lost contact up in the preamp area and needed replacing. Also some of the 25 mv signal wirewraps on the preamps lose contact sometimes, four were soldered in one of my organs professionally repaired. The orange and green wires are large current power supply wirewraps, not a problem. The silver and black wires are the problem, oxigen never sleeps and 25 mv can't burn oxide off.
Be sure that the motor cap is under 25 years old, or replace it. Located close to the motor. One burned the yellow wire down to one strand in my original organ in 1997, when it was replaced by a dealer tech who did not replace the wire or insulation. 3.3 uf 330 vac Genilec or epcos caps are available under the film cap category at newark & mouser. Crimp 90 deg flag terminals on the wires, don't solder them. Group them with a bread tie before cutting loose.
I use the high overtones to approximate the mellotron in Telstar or the shrieky organ in the Hatari version of Baby Elephant Walk.
Wait til you get the attack ("percussion") working on the upper keyboard. I like to use glock to do a celeste for Dance of the Sugar Plum Fairies. Glock is also a good Rhodes piano imitation for the intro to Free Bird etc. And when the string bass works, more e-caps usually, the bass is a lot of fun on rock ballads like De Call Me Da Breeze.
My organ after repair can be heard using 0888000000 on Yellow Bird at inbojat.tumblr.com
After I get the little whistle out by replacing 115 "harp" caps, I'll record some more.
Be sure to lube the TG two places, the scanners on the end of the TG if it has them, and the shaft of the round scanners one drop, if you have those. Use non-detergent non-zinc non-aluminum 5W or SUS24 oil, known to some as "hammond oil". Suppliers I trust of Hammond oil are Hammond-suzuki.com, tonewheelgeneral.com of KC, bborgan of IL, or Captain-foldback of Ontario. One oz is not enough. Other e-bay suppliers, you'll know if it had zinc if the dendrites grow on the pickups in 20 years. (most 5W oils do have zinc) Otherwise use SUS24 turbine oil in gallons from mcmaster.com, who also has a nice angled spout squeeze bottle that will fit behind the harp board on its side.
Have fun.
I've got three of them. None of them are up to date enough for the solid state preamps. Tubes all the way. All were working rather feebly and wimpily when I bought them 2010-2012, so I'd say reliability is not the problem.
The carbon comp resistors are not the problem, except there is a 10k in the power amp chassis that is always burned to 11.5k to 13.5 k. Look for a 10k with burned paint.
Replace with a 2 or 3 watt metal film resistor.
If the power amp cap has been particularly leaky, there is a 220 ohm resistor near the left wall that is burned. Check and replace as necessary. Only one of my 3 units needed it.
If you check them I think you'll find 99% of the carbon comp caps are in tolerance. At least if you organ was built in Chicago and they were still using mil-spec equivalent suppliers when yours was built. Mine are in spec. Units built in Holland, including the legendary X66, have mostly high value resistors by now.
The main problem, IMHO, is the electrolytic & tantalum caps. I replaced 71 of them in one unit, and the sound level tripled, the bass got much more commanding, and the trebles started to really shine when called for. With bad e-caps, even the ones up in the preamps on the back of the keyboards, the trebles are almost inaudible. I used film and a few 10 uf ceramic caps on the preamps where the film caps wouldn't fit. I did not remove the preamp boards, I just cut the axial wires, made hooks, and hooked the new caps over the old leads.
There was one pot that lost contact up in the preamp area and needed replacing. Also some of the 25 mv signal wirewraps on the preamps lose contact sometimes, four were soldered in one of my organs professionally repaired. The orange and green wires are large current power supply wirewraps, not a problem. The silver and black wires are the problem, oxigen never sleeps and 25 mv can't burn oxide off.
Be sure that the motor cap is under 25 years old, or replace it. Located close to the motor. One burned the yellow wire down to one strand in my original organ in 1997, when it was replaced by a dealer tech who did not replace the wire or insulation. 3.3 uf 330 vac Genilec or epcos caps are available under the film cap category at newark & mouser. Crimp 90 deg flag terminals on the wires, don't solder them. Group them with a bread tie before cutting loose.
I use the high overtones to approximate the mellotron in Telstar or the shrieky organ in the Hatari version of Baby Elephant Walk.
Wait til you get the attack ("percussion") working on the upper keyboard. I like to use glock to do a celeste for Dance of the Sugar Plum Fairies. Glock is also a good Rhodes piano imitation for the intro to Free Bird etc. And when the string bass works, more e-caps usually, the bass is a lot of fun on rock ballads like De Call Me Da Breeze.
My organ after repair can be heard using 0888000000 on Yellow Bird at inbojat.tumblr.com
After I get the little whistle out by replacing 115 "harp" caps, I'll record some more.
Be sure to lube the TG two places, the scanners on the end of the TG if it has them, and the shaft of the round scanners one drop, if you have those. Use non-detergent non-zinc non-aluminum 5W or SUS24 oil, known to some as "hammond oil". Suppliers I trust of Hammond oil are Hammond-suzuki.com, tonewheelgeneral.com of KC, bborgan of IL, or Captain-foldback of Ontario. One oz is not enough. Other e-bay suppliers, you'll know if it had zinc if the dendrites grow on the pickups in 20 years. (most 5W oils do have zinc) Otherwise use SUS24 turbine oil in gallons from mcmaster.com, who also has a nice angled spout squeeze bottle that will fit behind the harp board on its side.
Have fun.
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Thanks. I listened to Yellow Bird. Excellent sound sample. My Harp is weird, too. The e-caps have not been replaced yet.
There is some idle hiss at max. volume. There are some high value resistors before the amp, maybe some transistors are noisy, too. It is not the amp.
Dendrites were eliminated using pipe cleaners in contact boxes. Two thin contact wires were seized to the knife-edge of other contact tabs before busbar cleaning. There was one note that plainly pointed to that. That's gone but now one fundamental note dead. On bench ready to open up. Many screws.....
Also plan to modify cabinet to add fall-boards. I saw one guy did this on internet. Upper half sides need to be cut off and replaced. Big job. C3 cabinet too short because no control panel with tabs.
There is some idle hiss at max. volume. There are some high value resistors before the amp, maybe some transistors are noisy, too. It is not the amp.
Dendrites were eliminated using pipe cleaners in contact boxes. Two thin contact wires were seized to the knife-edge of other contact tabs before busbar cleaning. There was one note that plainly pointed to that. That's gone but now one fundamental note dead. On bench ready to open up. Many screws.....
Also plan to modify cabinet to add fall-boards. I saw one guy did this on internet. Upper half sides need to be cut off and replaced. Big job. C3 cabinet too short because no control panel with tabs.
Thanks for listening. I like the sound, also the one KSM27 mike on the one side. I've since found a second KSM27 mike, so less hiss will be in the next recording from a amped up dynamic supercardiode mike.
Oh, wow, a cabinet maker. Fall boards. I do wish it had something to keep the dust off. I had to use scrubbing bubbles on the keys.
My cabinet was destroyed in the move,the planned helper ran away after the truck was rented, it fell off the u-haul ramp upside down, that's the reason I bought #2. #9574 looks like Terminator after the gasoline fire. Top and one side are broken off. Sounds great, though.
I think your hiss will become insignificant as you get the volume up with better power supplies. (e-caps) Maybe also rectifier tubes, although I put the new ones away after trying them, they don't help anything on my unit 9574. I did expunge some hiss from my tube dynaco PAS2 preamp and ST70 amp by replacing carbon comp resistors >=100k with metal film. But they didn't have a motor whirring to cover up the hiss.
Sorry about the dentrites. Mine have no problems that way. Two had dealer service replacement capacitors, so probably they bought their hammond oil from the dealer.
One thing about the 7591 bias, many E100 owners report the diode blows in the -24 v circuit and makes the 7591's glow cherry red. One should really replace the 1967 diode with a 1n4003. Of course maybe by 1971 or 73 when yours was made, the reliability of silicon diodes was better. E100's date from 1965 on. My 1967&68 units haven't blown the minus 24 diode.
there was a H300 for sale in KY recently, I've been wondering if I should buy it for the taller cabinet. I have a set of ratchet drawbars to make 8 overtone percussion drawbars with, where the rhythm unit was installed would make a nice space for it. Rather than crippling guitar percussion for twos and banjo for threes (ala B/C3) I'd rather have individual control. Aren't op amp circuits fun!
One other thing, my country trailer unit got Mother mouse in the tab box and she ate some yellow & red wires up to make room for baby mice. I heard something crunching in the H100 end of the room last night 4AM. In the country I cut up tin cans and taped them over the holes where the wire harnesses enter the tab compartment, to stop the mice. Found a snake skin in there too, lots of action in that compartment. One needs to take the top off anyway to blow out the drawbar contacts with contact cleaner. BTW, bobmann107 of Utube (who has done H100 disassembly videos) says the late H100s with transistor percussion, had grease installed on the drawbar contacts. It dries up in 40 years. He recommends to take drawbars apart and clean the grease off mechanically with solvent. I don't think my early 67-68 units have it, I've got just a little scratching of the drawbars if I move when playing.
Glad to meet another fine clock/music fan.
Oh, wow, a cabinet maker. Fall boards. I do wish it had something to keep the dust off. I had to use scrubbing bubbles on the keys.
My cabinet was destroyed in the move,the planned helper ran away after the truck was rented, it fell off the u-haul ramp upside down, that's the reason I bought #2. #9574 looks like Terminator after the gasoline fire. Top and one side are broken off. Sounds great, though.
I think your hiss will become insignificant as you get the volume up with better power supplies. (e-caps) Maybe also rectifier tubes, although I put the new ones away after trying them, they don't help anything on my unit 9574. I did expunge some hiss from my tube dynaco PAS2 preamp and ST70 amp by replacing carbon comp resistors >=100k with metal film. But they didn't have a motor whirring to cover up the hiss.
Sorry about the dentrites. Mine have no problems that way. Two had dealer service replacement capacitors, so probably they bought their hammond oil from the dealer.
One thing about the 7591 bias, many E100 owners report the diode blows in the -24 v circuit and makes the 7591's glow cherry red. One should really replace the 1967 diode with a 1n4003. Of course maybe by 1971 or 73 when yours was made, the reliability of silicon diodes was better. E100's date from 1965 on. My 1967&68 units haven't blown the minus 24 diode.
there was a H300 for sale in KY recently, I've been wondering if I should buy it for the taller cabinet. I have a set of ratchet drawbars to make 8 overtone percussion drawbars with, where the rhythm unit was installed would make a nice space for it. Rather than crippling guitar percussion for twos and banjo for threes (ala B/C3) I'd rather have individual control. Aren't op amp circuits fun!
One other thing, my country trailer unit got Mother mouse in the tab box and she ate some yellow & red wires up to make room for baby mice. I heard something crunching in the H100 end of the room last night 4AM. In the country I cut up tin cans and taped them over the holes where the wire harnesses enter the tab compartment, to stop the mice. Found a snake skin in there too, lots of action in that compartment. One needs to take the top off anyway to blow out the drawbar contacts with contact cleaner. BTW, bobmann107 of Utube (who has done H100 disassembly videos) says the late H100s with transistor percussion, had grease installed on the drawbar contacts. It dries up in 40 years. He recommends to take drawbars apart and clean the grease off mechanically with solvent. I don't think my early 67-68 units have it, I've got just a little scratching of the drawbars if I move when playing.
Glad to meet another fine clock/music fan.
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Hiss is neither supply caps, diodes, nor tubes. It is probably silicon or carbon. Grounding the signal before the amp reduces hiss to Fender Twin Reverb levels. However, there a few e-caps in the preamps that have not been changed. There are also many Tantalum caps all around. Perhaps even the photo-resistors in the volume control but they are not directly in the signal path.
The reason I suspect high-value carbon resistors is that they are mounted inside the control panel--the location where all the heat rises from the tubes and power resistors. This machine can heat a room in winter. They are 330k, 1.5M, and 2.2M directly in the signal path.
The contacts and the drawbars are spotless.
I plan to go with replacing some of the transistors with parallel packages. The ones that you can hear in the speakers when tapped with a toothpick. This will eliminate the need to shake out noisy ones from a batch. Dead quiet, too.
The reason I suspect high-value carbon resistors is that they are mounted inside the control panel--the location where all the heat rises from the tubes and power resistors. This machine can heat a room in winter. They are 330k, 1.5M, and 2.2M directly in the signal path.
The contacts and the drawbars are spotless.
I plan to go with replacing some of the transistors with parallel packages. The ones that you can hear in the speakers when tapped with a toothpick. This will eliminate the need to shake out noisy ones from a batch. Dead quiet, too.
Being a tubeaholic, I also prefer these over the transistorized ones. Additionally, schematics for those transistor H-100's are hard to find, at least for me.
That reminds me of Klaus Wunderlich, an ex-GDR musician who literally knew all the tricks and performed every gut his H-100 offered to him.
Does that mean a missing tone from the TWG? If so, I don't see any chance to dismantle and to reassemble this unit correctly. Use a generator tone replacement instead, offered by Trek II.
Have fun with these instruments!
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keyboardpartner.de used to give away the schematic to the transistorized pedal/perc chassis , but I think you have to join their forum now to download a copy.
Before manuals were copywrited so here they are.
I don't think anybody has the schematic of the silent on turn-on board in the tab box.
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