122 Leslie rebuild, low switching voltage

[Crumb]

First post! Hello organ people!

I've recently built a 122 leslie amp & crossover. All new parts, tubes & sockets, transformers and everything.
Amp turns on and sounds clean, but not super loud. I've run it for several hours with no issues.... Except for the switching. The relay works, I've bench tested it with a current generator. The leslie connector kit works, i've tested it with other amps. I've also noticed that the preamp tubes don't glow as brightly as I typically see. I've checked voltages at all points and everything is within %5 tolerances of what the schematic says... Except relay voltage reads 20v when chorale is on. Just before the 12k 2w resistor it reads 60v, but when i bypass the resistor it reads 20v again. I'm at a loss here. I've tried different tubes. Power transformer gets hot, but i can still leave my hand on it comfortably, its not like I could fry an egg on it.

Thanks in advance, people.

[Jyvoipabo]

Hello,

It is not normal for the transformer to heat up.
Check that the fuse has not been oversized.
Measure all the HV voltages. Check the bridge rectifier.
Remove all lamps, disconnect one of the red HV wire and perform a 'no load' test.
Let him warm up long enough. It must remain quite cold.

The open frame relays tend to be a little lazy.
May be 60v-20v = 40V is not enough to make it.
If necessary it can be replaced can be replaced by Finder_40.61.9.060

JP

[muckelroy]

When you say the relay works, does it click when you switch speeds? Or does it only click when you apply coil voltage externally to it?

What is your screen voltage (the voltage on the upstream side of the 12k 2w resistor, and which goes to pin 4 of the 6550 tubes?)

What is your switching tube cathode voltage? It should be 25V.

Do you get a DC voltage at the grid of your switching tube when switched to chorale?

[Drawbar Dave]

Hello,

It is not normal for the transformer to heat up.
Check that the fuse has not been oversized.
Measure all the HV voltages. Check the bridge rectifier.
Remove all lamps, disconnect one of the red HV wire and perform a 'no load' test.
Let him warm up long enough. It must remain quite cold.

The open frame relays tend to be a little lazy.
May be 60v-20v = 40V is not enough to make it.
If necessary it can be replaced can be replaced by Finder_40.61.9.060

JP

The PT on my 147 gets as hot as a cup of coffee. There was a thread on here that I started last year. I bought a spare from classic Hammonds but the original is still working fine. So I don't think that is a problem.

[Crumb]

Switching tube has 25v at cathode. Grid voltage is 0v on tremolo, and 30v on chorale. Relay works on bench but not when installed in amp. Fuse is correct 1.5 slo-blo. 6550 screen voltage is 320v plate is 420v. Thanks for fast responses!

12au7 not lit up, but I got 6.3vac on across heaters. They are wired parallel with one grounded. It still plays and sounds good.

[Jyvoipabo]

Hello,

You got 20V instead of 25V Bias of the 6550.
The consumption is too high.
May be this is why the sound is very good and the transformer heats up.
We should try to find out why.
I suggest to check the bias circuit.
You can temporary remove the 220µ.

JP

[muckelroy]

12au7 not lit up, but I got 6.3vac on across heaters. They are wired parallel with one grounded. It still plays and sounds good.

Either the heater wiring is wrong or you have a bad 12AU7, or a faulty socket. The12AU7 should glow or it won't conduct and do its job.

[Crumb]

6550 tube bias is 25v at top of 150 resistor and 220uf cap.
I tried different 12AU7 tubes, wiring checks out too, the tube sockets are brand new ceramic ones. But now that you mention it, the 12AU7 tubes do seem excessively loose in them...
Maybe I'll put the old ones back in and see what happens.

[Jyvoipabo]

Hello,

The load off the 12AU7 is 12k + 5K(Relay) = 17k.
And it operate in switching mode (Off and On)

Off state (Vgk=-25V): Vak = 310-25 = 285V; I = 0

On State (Vgk=~0) : Vak =~90V; I~11,5mA (see 12AU7_Data)
and under this condition VacrossR12K = 140V; VRelay = 60V.

This is theorical values to ensure that a healthy relay and tube are properly working together.

JP

[Crumb]

9 pin mini tube sockets (white ceramic w/ gold pins) were the culprit. I replaced them and it's working now, power transformer still warm, but it now switches speeds, and is noticeably louder.
Ima stick with the plastic sockets i guess...
Thanks all for your help and knowledge!

[Drawbar Dave]

9 pin mini tube sockets (white ceramic w/ gold pins) were the culprit. I replaced them and it's working now, power transformer still warm, but it now switches speeds, and is noticeably louder.
Ima stick with the plastic sockets i guess...
Thanks all for your help and knowledge!

Well done for persevering!

[David Anderson]

Some cheap Chinese-made ceramic tube sockets look good, but are poorly-made. I've had to replace some in Hughes Kettner amps where the whole contact would come loose and pull out with the tube. Buy tube sockets from reputable dealers only.

I do definitely prefer Bakelite or Micanol plastic sockets for octal tubes in amps used for gigging. Ceramic sockets tend to result in more tubes with broken locator keys, resulting in tubes plugged in incorrectly, leading to fireworks.

[Codean]

Can any of you guys help me out with a 222 leslie (basically a 122). So I grabbed a CV with a 222 that is stuck on tremolo. I replaced all tubes, and relay. When I turn everything on now, my speakers are on chorale for about 5-10 sec then I hear a click and they change to trmolo. I know the leslie switch on the console is good (I metered it out) , so I'm thinkin its not getting the signal from the organ. Is there anything I can check on the organ side?

[David Anderson]

When a Leslie 122 is turned on, it's normal for it to go into Fast Speed immediately until the control voltage comes up enough to switch it to Slow. If the reverse is happening, I would suspect that you transposed some relay wires or have the plugs in the wrong sockets.

[Goff]

I do definitely prefer Bakelite or Micanol plastic sockets

Are there brand names of sockets that you'd recommend?

Sources?