If I recall correctly PR40 cabinets had a "room size" switch, which altered the bass response to suit different sized rooms.?
The bias is not changing since the resistor is between the cathodes and not between the cathodes and ground. Since the tubes are being driven out of phase with each other it will affect the gain of the stage. Kind of a neat hack to change the gain of both sides of the balanced amp at the same time with only a single pole switch..
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The bias is not changing since the resistor is between the cathodes and not between the cathodes and ground. Since the tubes are being driven out of phase with each other it will affect the gain of the stage. Kind of a neat hack to change the gain of both sides of the balanced amp at the same time with only a single pole switch..
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Things seem pretty quiet on the list lately, so I thought I'd ask a question:
What is the function of the "Bass Correction" switch, on a JR20 tone cab?
Looking at the schematic, it appears to switch a resistor (R35, 1K) in and out of series with the cathode resistors on the bass channel preamp tubes (V7 + V8, 6SJ7s).
Does that just function to change the bias on those tubes?? Or...?
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Re: PR20 tone cab problem
I have had problems with old tube sockets. The pins had pretty much lost their springiness so that they were not clamping the pins tightly. No amount of contact cleaning was able to fix that, and I had to wholesale replace the old sockets. Your problem sounds suspiciously similar - especially the loud thump, presumably as one of the tub pins loses and remakes contact with its socket pin. Likely the significant volume connection is that the tube starts to shake and loses contact with the socket again.
Having an issue with my PR-20 and was hoping for some guidance.
It plays fine and sounds great, with one exception: every so often I get a random surge of noise (static/crackle, pops, slight distortion, sometimes a kind of whistling), that goes on for 20-30 seconds or more.? This seems to happen particularly when I hit the amp with significant volume.
I think I have isolated the noise to the output tube (V11, 6BQ5) for the Reverb channel.
When the noise starts, I can lightly tap the top of that tube, which makes a loud thump, but it usually stops the ongoing noise.? Then it plays clean for awhile, sometimes as long as maybe 15 minutes before it acts up again.
Sometimes switching the reverb level with the knob on the side of the cabinet will make the noise stop as well.
I have tried changing that tube with no effect.? Could this be a problem with the tube socket?? I have hit it with contact cleaner several times, but the problem hasn't gone away.
I know guitar guys like to change tube sockets when they rebuild amps, but I've never had an issue with one.??So, should I suspect maybe C49 or C50?
I recapped this amp with the kit from Tonewheel General a few years back: <>?. So hopefully that rules out a filter cap issue.
Thanks for any advice.? When it's not acting up, the PR20 sounds great - especially in tandem with my "new" JR20!
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Re: PR20 tone cab problem
There may also be a cracked carbon comp resistor creating noise.
At this point you may have to shotgun all components connected to that particular output stage, or more.
Don Resor Sent from someone's iPhone
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On Feb 8, 2024, at 5:18 AM, Don R <organlists1@...> wrote:
? The problem may be either coupling capacitors, bias or control grid types. ? When a control grid capacitor goes bad the 6BQ5 output vacuum tube will be allowed to over conduct, or “run away”. ?When this happens the plate of this particular 6BQ5 will glow red hot. ?When this happens the vacuum tube will most likely be damaged.
Coupling capacitors can also cause noise. ?That and a driver vacuum tube. ?
These are filled with paper and ceramic capacitors. ?They may last a lifetime, but not indefinitely.
Don Resor Sent from someone's iPhone On Feb 7, 2024, at 9:54 PM, scott.brand@... wrote:
?Having an issue with my PR-20 and was hoping for some guidance.
It plays fine and sounds great, with one exception: every so often I get a random surge of noise (static/crackle, pops, slight distortion, sometimes a kind of whistling), that goes on for 20-30 seconds or more.? This seems to happen particularly when I hit the amp with significant volume.
I think I have isolated the noise to the output tube (V11, 6BQ5) for the Reverb channel.
When the noise starts, I can lightly tap the top of that tube, which makes a loud thump, but it usually stops the ongoing noise.? Then it plays clean for awhile, sometimes as long as maybe 15 minutes before it acts up again.
Sometimes switching the reverb level with the knob on the side of the cabinet will make the noise stop as well.
I have tried changing that tube with no effect.? Could this be a problem with the tube socket?? I have hit it with contact cleaner several times, but the problem hasn't gone away.
I know guitar guys like to change tube sockets when they rebuild amps, but I've never had an issue with one.??So, should I suspect maybe C49 or C50?
I recapped this amp with the kit from Tonewheel General a few years back:??.? So hopefully that rules out a filter cap issue.
Thanks for any advice.? When it's not acting up, the PR20 sounds great - especially in tandem with my "new" JR20!
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Re: PR20 tone cab problem
The problem may be either coupling capacitors, bias or control grid types. ? When a control grid capacitor goes bad the 6BQ5 output vacuum tube will be allowed to over conduct, or “run away”. ?When this happens the plate of this particular 6BQ5 will glow red hot. ?When this happens the vacuum tube will most likely be damaged.
Coupling capacitors can also cause noise. ?That and a driver vacuum tube. ?
These are filled with paper and ceramic capacitors. ?They may last a lifetime, but not indefinitely.
Don Resor Sent from someone's iPhone
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Show quoted text
On Feb 7, 2024, at 9:54 PM, scott.brand@... wrote:
?Having an issue with my PR-20 and was hoping for some guidance.
It plays fine and sounds great, with one exception: every so often I get a random surge of noise (static/crackle, pops, slight distortion, sometimes a kind of whistling), that goes on for 20-30 seconds or more.? This seems to happen particularly when I hit the amp with significant volume.
I think I have isolated the noise to the output tube (V11, 6BQ5) for the Reverb channel.
When the noise starts, I can lightly tap the top of that tube, which makes a loud thump, but it usually stops the ongoing noise.? Then it plays clean for awhile, sometimes as long as maybe 15 minutes before it acts up again.
Sometimes switching the reverb level with the knob on the side of the cabinet will make the noise stop as well.
I have tried changing that tube with no effect.? Could this be a problem with the tube socket?? I have hit it with contact cleaner several times, but the problem hasn't gone away.
I know guitar guys like to change tube sockets when they rebuild amps, but I've never had an issue with one.??So, should I suspect maybe C49 or C50?
I recapped this amp with the kit from Tonewheel General a few years back:??.? So hopefully that rules out a filter cap issue.
Thanks for any advice.? When it's not acting up, the PR20 sounds great - especially in tandem with my "new" JR20!
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Having an issue with my PR-20 and was hoping for some guidance.
It plays fine and sounds great, with one exception: every so often I get a random surge of noise (static/crackle, pops, slight distortion, sometimes a kind of whistling), that goes on for 20-30 seconds or more.? This seems to happen particularly when I hit the amp with significant volume.
I think I have isolated the noise to the output tube (V11, 6BQ5) for the Reverb channel.
When the noise starts, I can lightly tap the top of that tube, which makes a loud thump, but it usually stops the ongoing noise.? Then it plays clean for awhile, sometimes as long as maybe 15 minutes before it acts up again.
Sometimes switching the reverb level with the knob on the side of the cabinet will make the noise stop as well.
I have tried changing that tube with no effect.? Could this be a problem with the tube socket?? I have hit it with contact cleaner several times, but the problem hasn't gone away.
I know guitar guys like to change tube sockets when they rebuild amps, but I've never had an issue with one.??So, should I suspect maybe C49 or C50?
I recapped this amp with the kit from Tonewheel General a few years back:??.? So hopefully that rules out a filter cap issue.
Thanks for any advice.? When it's not acting up, the PR20 sounds great - especially in tandem with my "new" JR20!
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I had to replace a couple of keys on my 'D' which is only slightly later. I used keys from an M3. It turns out they are about 1/16" shorter than the original keys. If you replace them all it wouldn't be noticeable I guess.
So, I had an "aha" moment about the BCV that I posted about earlier - the one I acquired late last year.
...
With all that said: can anyone sell me some smooth keycaps? I have 2 octaves I had set aside just in case of damage to my old C3. So, I would need 8 octaves total.
If anyone has some for sale, please contact me via email: scott (dot) brand (at) aya (dot) yale (dot) edu.
Cheers guys!
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So, I had an "aha" moment about the BCV that I posted about earlier - the one I acquired late last year.
It's from 1938, so it should certainly have the "ratcheting" drawbars, in fact unless I miss my guess they should have been the chrome type, with the numbers actually stamped in.
...But in fact, someone has evidently been at this organ before me: much to my surprise it actually has smooth drawbars.
It does however still have the "sharp-edged" keycaps.? I was actually struck by just how much of an edge they have - "palm smears" are a little problematic on these.
Now, ordinarily my impulse would have been to preserve everything as original, especially given the venerable age of this instrument.? (It's actually so early the manufacturer's tag reads "Hammond Clock Co." instead of "Hammond Organ Co."!)
But now it looks like that ship has already sailed - those original chrome drawbars are long gone.? So, I thought I'd go ahead and make this a full-on "player grade" B, by changing out the keycaps for the later, smooth-edged kind.
With all that said: can anyone sell me some smooth keycaps?? I have 2 octaves I had set aside just in case of damage to my old C3.? So, I would need 8 octaves total.??
If anyone has some for sale, please contact me via email: scott (dot) brand (at) aya (dot) yale (dot) edu.
Cheers guys!
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Thank you for the advice. I have booked it in for repair.
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On 1 Feb 2024, at 12:21, Chris Clifton via groups.io <clifton.christopher@...> wrote:
?
PS. There is also a mains fuse that protects the amplifier circuits alone, motors will still run if this fuse has blown. This is FS2 in the schematic, and is the middle one of the three fuses on the power supply circuit board. In my experience, this rarely
blows unless there is a fault in the amplifier, but worth checking.
On 01/02/2024 12:13, Chris Clifton wrote:
I don't have 330 schematic in my collection, but I don't believe that there is a speaker fuse. I've had a look at the electrically similar 820 schematic (main difference is no horn speaker every thing goes through a full range 12" speaker in the bottom of
the cabinet). One fault I seem to recall occurring quite frequently in similar Leslie amps is no +28.5 volt supply to the driver stages of the power amp. Often caused by an open circuit R3, 8 ohm 10 watt, resistor on the power supply chassis.
I've found a schematic at . Please remember that there is mains voltage in the power supply, take care if you attempt diagnosis your self. If you don't have the necessary skill and experience, don't even try.
On 01/02/2024 11:04, George Matthews wrote:
Hello,
I have a Leslie 330 and all of a sudden I'm am not getting any sound. Motors and everything working normally just no sound output. Is there an output fuse??
If any one has any suggestions?please let me know.
Thank you
George
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PS. There is also a mains fuse that protects the amplifier
circuits alone, motors will still run if this fuse has blown. This
is FS2 in the schematic, and is the middle one of the three fuses
on the power supply circuit board. In my experience, this rarely
blows unless there is a fault in the amplifier, but worth
checking.
On 01/02/2024 12:13, Chris Clifton
wrote:
I don't have 330 schematic in my collection, but I don't
believe that there is a speaker fuse. I've had a look at the
electrically similar 820 schematic (main difference is no horn
speaker every thing goes through a full range 12" speaker in the
bottom of the cabinet). One fault I seem to recall occurring
quite frequently in similar Leslie amps is no +28.5 volt supply
to the driver stages of the power amp. Often caused by an open
circuit R3, 8 ohm 10 watt, resistor on the power supply chassis.
I've found a schematic at .
Please remember that there is mains voltage in the power supply,
take care if you attempt diagnosis your self. If you don't have
the necessary skill and experience, don't even try.
On 01/02/2024 11:04, George Matthews
wrote:
Hello,
I have a Leslie 330 and all of a sudden I'm am
not getting any sound. Motors and everything working
normally just no sound output. Is there an output fuse??
If any one has any suggestions?please let
me know.
Thank you
George
--
--
|
I don't have 330 schematic in my collection, but I don't believe
that there is a speaker fuse. I've had a look at the electrically
similar 820 schematic (main difference is no horn speaker every
thing goes through a full range 12" speaker in the bottom of the
cabinet). One fault I seem to recall occurring quite frequently in
similar Leslie amps is no +28.5 volt supply to the driver stages
of the power amp. Often caused by an open circuit R3, 8 ohm 10
watt, resistor on the power supply chassis.
I've found a schematic at
.
Please remember that there is mains voltage in the power supply,
take care if you attempt diagnosis your self. If you don't have
the necessary skill and experience, don't even try.
On 01/02/2024 11:04, George Matthews
wrote:
Hello,
I have a Leslie 330 and all of a sudden I'm am
not getting any sound. Motors and everything working normally
just no sound output. Is there an output fuse??
If any one has any suggestions?please let
me know.
Thank you
George
--
|
Hello,
I have a Leslie 330 and all of a sudden I'm am not getting any sound. Motors and everything working normally just no sound output. Is there an output fuse??
If any one has any suggestions?please let me know.
Thank you
George
|
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The symptoms you describe suggest a mechanical problem with the swell pedal. When you move the swell pedal, does the shaft sticking out of the side of the swell box turn? Try disconnecting the lever from the swell box and turning the shaft by hand, it should
turn easily, and change the organ volume as it moves.?
I ended up after a couple of years with an m102 but it had some issues. i recently acquired another m102 in much better shape. It's only problem it seems is that the pedal seems to have on effect on volume. It plays at roughly the same full volume of the
old organ. the volume soft tab works and the drawbars all work. the lever behind the pedal works.?
any suggestion for next steps.... ie... a specific tube maybe? any suggestions would be appreciated.?
Thank you
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The symptoms you describe suggest a mechanical problem with the swell pedal. When you move the swell pedal, does the shaft sticking out of the side of the swell box turn? Try disconnecting the lever from the swell box and turning the shaft by hand, it should
turn easily, and change the organ volume as it moves.?
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Show quoted text
I ended up after a couple of years with an m102 but it had some issues. i recently acquired another m102 in much better shape. It's only problem it seems is that the pedal seems to have on effect on volume. It plays at roughly the same full volume of the
old organ. the volume soft tab works and the drawbars all work. the lever behind the pedal works.?
any suggestion for next steps.... ie... a specific tube maybe? any suggestions would be appreciated.?
Thank you
|
I ended up after a couple of years with an m102 but it had some issues. i recently acquired another m102 in much better shape. It's only problem it seems is that the pedal seems to have on effect on volume. It plays at roughly the same full volume of the old organ. the volume soft tab works and the drawbars all work. the lever behind the pedal works.?
any suggestion for next steps.... ie... a specific tube maybe? any suggestions would be appreciated.?
Thank you
|
It is quite a while since I made the list of organs needing new homes.? One M3? and one L100? still operational.? The M2s need work. As far as I can determine, the mechanical parts are fine though needing oil.? Capacitors would be the main job to get them back to life. A one ton van would likely haul all of them although some disassembly would be required. The XTP has gone to a good home locally. That leaves 2 M2s, 1 M3, and 2 L100s although only one is operational.?
I expect no money for these and could only arrange for manpower to load them.? I am past the lifting stage.? I do have a new location for them beginning this summer as the building owner needs them gone.? I do have another dedicated waterproof building on the farm to keep them for now.? There are also a couple of smaller transistorized organs that do not work but have plenty of useful parts.
Thanks for reading, Gord, VE5UJ
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Re: Leslie 330 - theoretical question
Ah I see, thank you for the explanation, Chris.? And you are quite right: the Leslie had sat for several months, plugged in but without being powered up.
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Re: Leslie 330 - theoretical question
T2 powers the control and standby circuit. When pins 5 &6 relay 1 is activated switching the power on to the main circuits. With no power to the control circuit due to the faulty capacitor, the rest of the Leslie couldn't turn on.
Thought just occurred to me. Is it possible that the Leslie was left for a long time (weeks or even months) plugged into the mains but not fully powered up? In this condition T2 and associated components for the control circuit would have power applied continuously,
possibly leading to the failure of that capacitor.
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Thank you Chris and Christoph for your responses.? It sounds like it's probably worth taking a chance and plugging the 330 into the B3000 again.
As a matter of interest I think we can rule out any issue with the 28 VDC.? That was actually my first thought as well, but then I realized I had used an 11-pin cable with only 9 conductors, i.e. in a pinch one day I had converted a 9-conductor cable for use
in 11-pin systems by changing out the terminal hardware, but just omitting the connections for pins 9 and 11.
Looking at the schematic I think I can understand why a faulty C1 would cause the "no motors" symptom without blowing a fuse.? But I don't see the connection in terms of how it could cause the "no audio" state, since the amplifier is powered through T1 and
not T2 - ?
In any case I'll take the plunge and try the B3000-to-330 hookup again; will report back.? Thanks again.
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Re: Leslie 330 - theoretical question
Quick update: you guys were right!? I plugged the B3000 and the Leslie 330 together, and everything works fine.? It actually sounds great!? More tonewheel-like than I had expected.
Anyway thanks again, I appreciate all the help.
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Anthony Leeman