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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: 5280
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: 653
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: 5280
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: 653
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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Posts: 3195
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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: L111, M3, BC, CV, Franken CV, A100, B3
Leslie: 710, 760, 51C, 147, 145, 122, 31H
Yamaha: CP4, DGX-620, DX7II-FD-E!, PF85
Roland: VR-09
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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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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: L111, M3, BC, CV, Franken CV, A100, B3
Leslie: 710, 760, 51C, 147, 145, 122, 31H
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: 653
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: 3195
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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: L111, M3, BC, CV, Franken CV, A100, B3
Leslie: 710, 760, 51C, 147, 145, 122, 31H
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: 5280
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: 5280
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: 3195
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: L111, M3, BC, CV, Franken CV, A100, B3
Leslie: 710, 760, 51C, 147, 145, 122, 31H
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: 5280
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: 512
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: 5280
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: 160
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
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Registered: 04/11/05
Posts: 512
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?
_________________________
"Show me all the blueprints. I'm serious now, show me all the blueprints."
My homemade instruments

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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: 5280
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: 5280
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: 3195
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: L111, M3, BC, CV, Franken CV, A100, B3
Leslie: 710, 760, 51C, 147, 145, 122, 31H
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: 5280
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
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Registered: 02/10/01
Posts: 5280
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: 3195
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: L111, M3, BC, CV, Franken CV, A100, B3
Leslie: 710, 760, 51C, 147, 145, 122, 31H
Yamaha: CP4, DGX-620, DX7II-FD-E!, PF85
Roland: VR-09
Band Site: http://DrBombay.ca/

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#2894879 - 12/09/17 03:42 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: WesG]
Markyboard Offline
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Registered: 02/10/01
Posts: 5280
Loc: Springfield, Virginia
Here's an update: I'm fairly certain I nailed this to a bad T4 transformer. The percussion circuit has 3 transformers and amplifier stages in series. I got fooled into thinking it was the last transformer (T6) in the chain; what looked like a good input signal with no corresponding output was actually just noise coupling on the input winding. It wasn't until by luck the frequency of working periods increased and I could see what these percussion signals are supposed to look like that things got a bit easier. That and some awesome help offline from WesG and also Rick from Tonewheel General Hospital. Still this failed intermittent transformer is acting very strange and made this a very difficult problem to diagnose. Oh well- learned tons about amps and how these organs work. Should be time well spent in future endeavors. Also confirmed several times those high voltages do kick your ass ( no joke).


I snagged an AO-29 preamp on eBay for the replacement T4 Transformer. And this whole Hard to get Parts theme got me thinking about other stuff that may fail and so...

ROAD TRIP!


He's throwing n a second M3 for $45. Provided it will fit in my rental truck.

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#2894882 - 12/09/17 03:53 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: Markyboard]
WesG Offline
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Registered: 02/16/13
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Loc: Inverary, ON, Canada
What are you renting? A Chevy City Express would be an excellent choice. Good mileage, low deck, enough room for a console and leslie. Trucks suck IMO, lifting even an M3 can be a real bitch.
_________________________
Hammond: L111, M3, BC, CV, Franken CV, A100, B3
Leslie: 710, 760, 51C, 147, 145, 122, 31H
Yamaha: CP4, DGX-620, DX7II-FD-E!, PF85
Roland: VR-09
Band Site: http://DrBombay.ca/

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#2894888 - 12/09/17 04:14 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: Markyboard]
davedoerfler Offline
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Loc: thin ice
Originally Posted By: Markyboard
ROAD TRIP!


Damn. 500 miles round trip. Better go before it starts snowing.
Oops, too late. facepalm laugh
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Never be cruel,never be cowardly,and never eat pears.Remember:hate is always foolish and love is always wise.Always try to be nice,and never fail to be kind.Oh and you mustn’t tell anyone your name.

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#2894890 - 12/09/17 04:42 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: WesG]
Markyboard Offline
MP Hall of Fame Member

Registered: 02/10/01
Posts: 5280
Loc: Springfield, Virginia
Originally Posted By: WesG
What are you renting? A Chevy City Express would be an excellent choice. Good mileage, low deck, enough room for a console and leslie. Trucks suck IMO, lifting even an M3 can be a real bitch.

Damn- I knew I should have held onto that canoe. laugh

Originally Posted By: davedoerfler
Originally Posted By: Markyboard
ROAD TRIP!


Damn. 500 miles round trip. Better go before it starts snowing.
Oops, too late. facepalm laugh


All my Hammond/Leslie acquisitions involve a road trip - usually more miles than this. A little snow ain't gonna stop me. So...what are you doing next Saturday? poke gofish

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#2895224 - 12/11/17 04:08 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: Markyboard]
davedoerfler Offline
KCFF League Champion 2017
MP Hall of Fame Member

Registered: 12/27/12
Posts: 6688
Loc: thin ice
Originally Posted By: Markyboard
So...what are you doing next Saturday? poke gofish


gofish (I wish)
actually, I'll be working, but I will use "The Force" to help you. cool
_________________________
Never be cruel,never be cowardly,and never eat pears.Remember:hate is always foolish and love is always wise.Always try to be nice,and never fail to be kind.Oh and you mustn’t tell anyone your name.

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#2895268 - 12/11/17 07:21 PM Re: Hammond B3 (A028) - Hard to get Parts [Re: davedoerfler]
Markyboard Offline
MP Hall of Fame Member

Registered: 02/10/01
Posts: 5280
Loc: Springfield, Virginia
Originally Posted By: davedoerfler
Originally Posted By: Markyboard
So...what are you doing next Saturday? poke gofish


gofish (I wish)
actually, I'll be working, but I will use "The Force" to help you. cool



Thanks Obi-Wan! Btw I just got home this evening and changed out the T4 transformer with a pull from the first of 4 A0-29s pre-amps purchased over the last week. Percussion sounding good so far.

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#2896371 - 12/17/17 08:07 AM Re: Hammond B3 (A028) - Hard to get Parts [Re: Markyboard]
Markyboard Offline
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Registered: 02/10/01
Posts: 5280
Loc: Springfield, Virginia
(Long Story Ahead)
Successful road trip although I ended up with a pick-up truck after the rental company screwed me on my so-called reserved cargo van. About 9 hour round trip - not too bad. The guy had a nice full on recording studio with a huge vintage Neve board and lots of other cool stuff. His engineer was all too happy to show me around which was good because when the seller showed up he was all business - but nice enough.

Went to the storage room and cleared out a few other nicer Hammonds/Leslies to get the M3s through the door and up on the truck; just the 2 of us (barely, still got a good case of Hammond back). We used a couple of ramps and rolled each using a dolly onto the pick-up bed. Didn't think it would work but fortunately it did. F**ken rental car company mad. My son, his friend and a neighbor helped when I got home.

I'm now thinking I'll keep the better of the 2 M3s intact - fix it up with parts from the other M3 and the additional preamps I scored over the last week:


This one for parts.



I'm happy to have a spare percussion switch module as I near screwed up one of the leaf switches for the percussion volume in my B3 last week. Fortunately I only bent half of the U-shaped metal contact (on opposite side of circuit board) so it still works well. And I fixed the flaky decay switch by soldering on a small piece of wire to one side of the contact. Works great now but man those things are delicate.




Despite what many complain about, removing the circuit board is not bad as long as you're careful with the contacts. No need to remove the metal springs on the plastic switches themselves - which is a pain to reinstall (I did remove one thinking the tension spring was part of the problem - it wasn't). The hardest part in removing just the circuit board is loosening the cable clamps in the back and feeding the cable slack to that side in order to have enough room to work.


And finally the 2 separately purchased pre-amps for parts:

I already grabbed the T4 transformer which is now in use in my B3. All my initially reported low voltages are back to nominal (or even slightly above) with this transformer replacement- so it was the bad transformer sucking a lot of juice and loading things down. Btw Wes that T5 transformer in the container has your name on it - PM me your address


My final mod is to replace the power transformer and fuse it. Got the new part yesterday and will install shortly. But this B3 sounds better than I remember and I'm happy that it gets more than loud enough again - something it suffered for quite some time, apparently due to those low voltages .







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#2896374 - 12/17/17 08:17 AM Re: Hammond B3 (A028) - Hard to get Parts [Re: Markyboard]
davedoerfler Offline
KCFF League Champion 2017
MP Hall of Fame Member

Registered: 12/27/12
Posts: 6688
Loc: thin ice
Great story, thanks for sharing. thu
_________________________
Never be cruel,never be cowardly,and never eat pears.Remember:hate is always foolish and love is always wise.Always try to be nice,and never fail to be kind.Oh and you mustn’t tell anyone your name.

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