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#2890069 - 11/13/17 11:13 AM Hammond B3 (A028) - Hard to get Parts
Markyboard Offline
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Registered: 02/10/01
Posts: 5094
Loc: Springfield, Virginia
I've been troubleshooting the percussion in my B3 which is outputting at a very low level. It was intermittent for a while but eventually went steady state remaining at the low volume. Looks like my T6 transformer died. Fortunately I have a "pull" on the way but it appears all 3 percussion transformers are difficult if not impossible to find.

Is there no modern equivalent of these xformers? Anyone know the specs on them? Googling I saw a similar question on the Organ Forum from a while back, albeit no answer.

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#2890073 - 11/13/17 11:24 AM Re: Hammond B3 (A028) - Hard to get Parts [Re: Markyboard]
GRollins Offline
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Registered: 09/01/17
Posts: 353
When your new one comes in, measure the voltages and post them. It may be that a match can be found.

Grey
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#2890077 - 11/13/17 11:31 AM Re: Hammond B3 (A028) - Hard to get Parts [Re: GRollins]
Markyboard Offline
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Registered: 02/10/01
Posts: 5094
Loc: Springfield, Virginia
Would that not just tell what it's operating at, and not the spec?

Btw the input to mine is about 160V depending on the position of the percussion switches. Rick from TWGH mentioned the output should be at about 200V. Mine shows a big goose egg at the output.


Edited by Markyboard (11/13/17 11:35 AM)

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#2890083 - 11/13/17 12:08 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: Markyboard]
GRollins Offline
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Registered: 09/01/17
Posts: 353
Measure it before putting it in--no load conditions.

Grey
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#2890091 - 11/13/17 12:45 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: GRollins]
WesG Offline
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Registered: 02/16/13
Posts: 3057
Loc: Inverary, ON, Canada
I'm about 99.44% sure the percussion transformers in an AO-29 are identical.

Grey - measuring voltages on these is of limited utility. They are essentially interstage coupling transformers.

http://bentonelectronics.com/wp-content/uploads/2012/01/ao28schematic.gif


Edited by WesG (11/13/17 12:49 PM)
_________________________
Hammond: Split L111, '58 M3, '59 B3, Northern DV
Leslie: 760, 51C, 147, 145
Yamaha: CP4, DGX-620, DX7II-FD-E!, PF85
Roland: VR-09
Band Site: http://DrBombay.ca/

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#2890092 - 11/13/17 12:48 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: WesG]
WesG Offline
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Registered: 02/16/13
Posts: 3057
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Markyboard, how are you measuring the output? The output from T6 looks like it should have no DC component and the AC component looks to me like it would be in the mVs, as it feeds the first grid of V4 (12AX7).
_________________________
Hammond: Split L111, '58 M3, '59 B3, Northern DV
Leslie: 760, 51C, 147, 145
Yamaha: CP4, DGX-620, DX7II-FD-E!, PF85
Roland: VR-09
Band Site: http://DrBombay.ca/

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#2890095 - 11/13/17 12:57 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: WesG]
GRollins Offline
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Registered: 09/01/17
Posts: 353
Originally Posted By: WesG
Grey - measuring voltages on these is of limited utility. They are essentially interstage coupling transformers.


I see what you're saying. I'll bow out.

Grey
_________________________
I'm not interested in someone's ability to program. I'm interested in their ability to compose and play.

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#2890097 - 11/13/17 01:05 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: GRollins]
WesG Offline
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Posts: 3057
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Markyboard - what is the voltage on the center tap of T6? And, do you have a scope?

I'm guessing you're going to find that the CT T6 voltage is around 165V, which should be the same as the junction of R97, R98 and C60. If THAT test point is also at ~165V, then your low-voltage complaint is due to a fault in the power supply. Are your filter caps 60 years old? Has R97 drifted high?

Have you tried swapping V5 and V6? Have you replaced V7 with a known good one?

Is C30 by any chance 60 years old?


Edited by WesG (11/13/17 01:10 PM)
_________________________
Hammond: Split L111, '58 M3, '59 B3, Northern DV
Leslie: 760, 51C, 147, 145
Yamaha: CP4, DGX-620, DX7II-FD-E!, PF85
Roland: VR-09
Band Site: http://DrBombay.ca/

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#2890111 - 11/13/17 02:22 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: WesG]
Markyboard Offline
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Registered: 02/10/01
Posts: 5094
Loc: Springfield, Virginia
Originally Posted By: WesG
Markyboard - what is the voltage on the center tap of T6? ~150V going to ~165V with upper reg note pressed And, do you have a scope? Yes (haven't used it on this yet - please let me know what I'm looking for)

I'm guessing you're going to find that the CT T6 voltage is around 165V, which should be the same as the junction of R97, R98 and C60. If THAT test point is also at ~165V, then your low-voltage complaint is due to a fault in the power supply. Are your filter caps 60 years old? No I refurbed this just a few years ago. Has R97 drifted high? Will check tomorrow

Have you tried swapping V5 and V6? Have you replaced V7 with a known good one? Yup replaced these all with new tubes as part of my troubleshooting - no joy.

Is C30 by any chance 60 years old? I think this got replaced as part of refurbing - will check.



Question: are the points labeled +205 , +37 and +33 supposed to indicate expected voltages?

Much appreciated!

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#2890114 - 11/13/17 02:31 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: WesG]
Markyboard Offline
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Registered: 02/10/01
Posts: 5094
Loc: Springfield, Virginia
Originally Posted By: WesG
Markyboard, how are you measuring the output? The output from T6 looks like it should have no DC component and the AC component looks to me like it would be in the mVs, as it feeds the first grid of V4 (12AX7).


I used my dvm on both DC and AC. I recall seeing a small value on the AC setting in the mV range so maybe this "hard to find" part is Ok after all. Will check voltages again tomorrow.

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#2890115 - 11/13/17 02:35 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: Markyboard]
WesG Offline
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Registered: 02/16/13
Posts: 3057
Loc: Inverary, ON, Canada
The test points in your power supply should be CLOSE to the expected voltages, after compensating for your current wall voltage. The manual was done for a 117V supply, but many homes now are much higher, resulting in equivalently higher power supply voltages.

To test the transformer, watch its primary winding (left side of schematic - with the center tap). You should see a couple of hundred volts DC with a small AC waveform riding on it when you trigger the percussion. Please make sure your scope and probe is rated for at least 300V. Then you should the same AC waveform, at a different amplitude, on the secondary with no DC offset.

I don't know the winding ratio, but typically, a winding either works or it doesn't.

I don't know what's wrong with your organ, but my spidey sense is telling me that the amplitude of the waveform (irrespective of the DC offset) is too low on the primary side of T6.

Look at components around V5. V6 controls the envelope.
_________________________
Hammond: Split L111, '58 M3, '59 B3, Northern DV
Leslie: 760, 51C, 147, 145
Yamaha: CP4, DGX-620, DX7II-FD-E!, PF85
Roland: VR-09
Band Site: http://DrBombay.ca/

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#2890120 - 11/13/17 02:51 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: WesG]
Markyboard Offline
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Registered: 02/10/01
Posts: 5094
Loc: Springfield, Virginia
Thanks Wes - will post my findings tomorrow. Btw 60 years old? How did you know my B3 is a 57? idk

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#2890123 - 11/13/17 02:53 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: WesG]
bourniplus Offline
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Registered: 04/11/05
Posts: 502
Loc: Québec
You guys are speaking chinese for me so this is above my electronics skills, but have you tried zapping with a 9v battery to clear dendrite??
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#2890124 - 11/13/17 03:02 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: bourniplus]
Markyboard Offline
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Registered: 02/10/01
Posts: 5094
Loc: Springfield, Virginia
Good thought- but this does not appear to be a dendrite issue although I did zap it anyway as called out on the well documented logic flow procedure. However I was skeptical based on the intermittent characteristic. Also I don't recall ever seeing that dendrites would lower the volume of the percussion.

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#2890128 - 11/13/17 03:08 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: bourniplus]
JB Sherry Offline
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Registered: 03/17/07
Posts: 157
Loc: Saugerties, NY
I'm loving it, though it's almost all above my pay grade as well. And, I had to google to confirm that dendrite growth can also affect the percussion switch assembly (knew about the Vibrato Scanner).

Awaiting the next installment...
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#2890130 - 11/13/17 03:13 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: Markyboard]
bourniplus Offline
Gold Member

Registered: 04/11/05
Posts: 502
Loc: Québec
Originally Posted By: Markyboard
I don't recall ever seeing that dendrites would lower the volume of the percussion.


I seem to remember it's what happened on my A100. Have you tried with two 9v batteries?
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#2890132 - 11/13/17 03:19 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: bourniplus]
Markyboard Offline
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Registered: 02/10/01
Posts: 5094
Loc: Springfield, Virginia
Yeah, thinking about it there's no reason why dendrites couldn't short the perc. volume switch. But yes, I did use 2 - 9 v batteries as I was seeing some impedance in the path being measured. It did get rid of that impedance, but didn't help the problem. However maybe I mitigated another problem brewing.

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#2890299 - 11/14/17 02:33 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: Markyboard]
Markyboard Offline
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Registered: 02/10/01
Posts: 5094
Loc: Springfield, Virginia
Originally Posted By: Markyboard
[quote=WesG]Markyboard - what is the voltage on the center tap of T6? ~150V going to ~165V with upper reg note pressed And, do you have a scope? Yes (haven't used it on this yet - please let me know what I'm looking for)

I'm guessing you're going to find that the CT T6 voltage is around 165V, which should be the same as the junction of R97, R98 and C60. Update: True - it measures ~165V. If THAT test point is also at ~165V, then your low-voltage complaint is due to a fault in the power supply. Are your filter caps 60 years old? No I refurbed this just a few years ago. Has R97 drifted high? Will check tomorrow. Update : measured in circuit at ~4.1K and creeping up with capacitance expected effects (i.e. I thinks it's OK).

Have you tried swapping V5 and V6? Have you replaced V7 with a known good one? Yup replaced these all with new tubes as part of my troubleshooting - no joy.

Is C30 by any chance 60 years old? I think this got replaced as part of refurbing - will check.
Update: Both C30 and C31 were replaced a couple years ago.



I'm seeing approx 350V at pin 7 of the V8 tube although there was a brief period where it read a nominal 374V so I believe something's loading down that point. I'll probably start with replacing the filter can caps (I have spares) although both were replaced a couple of years ago as well. But I can imagine a flaky cap with a soft short developing.

Btw the wall voltage measured at the T7 transformers is approx 119V. So yeah, good call Wes. Something's pulling down my supply.

I also just pulled R91 at the C56 side and I'm reading approx 488V (unloaded). I assume that's right? idk I think next step is to lift R97.

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#2890305 - 11/14/17 02:50 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: Markyboard]
WesG Offline
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Registered: 02/16/13
Posts: 3057
Loc: Inverary, ON, Canada
The brief period where it read 374V, during power up? If so, normal, B+ will drop as tubes heat up.

Just about anything in the amp can, in theory, drag down your B+. You can get clues by examining the voltages at the different test points in your power supply, though.

It's also possible you're chasing a red herring (fun, aren't I?) and you just have a larger than usual B+ load.......you're 20% low right now, which is right on the cusp of being maybe-acceptable.

Say, how is your Leslie switching done? Is it a 122? If so, and if you are getting B+ from the AO28, disconnect it for diagnostic purposes.

What's your voltage drop across R91? You can figure out the load on B+, both expected and actual, by watching that figure.

Do you have close to 340 VRMS across the secondary T7?

Wes
_________________________
Hammond: Split L111, '58 M3, '59 B3, Northern DV
Leslie: 760, 51C, 147, 145
Yamaha: CP4, DGX-620, DX7II-FD-E!, PF85
Roland: VR-09
Band Site: http://DrBombay.ca/

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#2890318 - 11/14/17 04:10 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: WesG]
Markyboard Offline
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Registered: 02/10/01
Posts: 5094
Loc: Springfield, Virginia
I don't believe the 374V was a transient or a quick turn on artifact. It was present for a good long time. I'm also not sure if I caused it to drop to 350 or so, probably not.

I had to go back and study all that B+ connectivity thought the 6122 interface to the Leslie 122 (x2). In fact I was all excited thinking that driving 2 122s was causing the lower voltage. But disconnecting both only increased the voltage to maybe 354 V . I'll see if I can further isolate things tomorrow. It's a bitch to unsolder some of those point to point components. Not sure why they had to wrap them around the post so many times mad

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#2890319 - 11/14/17 04:15 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: WesG]
Markyboard Offline
MP Hall of Fame Member

Registered: 02/10/01
Posts: 5094
Loc: Springfield, Virginia
Originally Posted By: WesG

Do you have close to 340 VRMS across the secondary T7?

Wes


Yes- actually closer to 350V

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#2890348 - 11/14/17 08:03 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: Markyboard]
WesG Offline
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Registered: 02/16/13
Posts: 3057
Loc: Inverary, ON, Canada
I was thinking the cap in the kit might be bad, but after studying the schematic, I see that it cannot drag down the B+ more than a trivial amount. Even if the cap were a dead short, there's still about 150K of resistance between B+ and GND.

Is your 350VRMS with the rectifier and other tubes in place? If so - then the very first thing I would check is that R91 still close to 900 ohms, and I would check the voltage drop across R91 ....and the condition of that percussion cap I told you about.

Hammond stuff was soldered to NASA satellite-build standards or something....which is why they still work. And why I try to puzzle out problems without unsoldering anything. smile
_________________________
Hammond: Split L111, '58 M3, '59 B3, Northern DV
Leslie: 760, 51C, 147, 145
Yamaha: CP4, DGX-620, DX7II-FD-E!, PF85
Roland: VR-09
Band Site: http://DrBombay.ca/

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