21h up and running but not very loud

[Jamfu]

I Replaced all the capacitors , and tubes, and managed to not let the smoke out of any parts. I plugged it in to my organ . It sounds fine but there's not a lot of gain. Its not breaking up at all even though I turn it all the way up. It's a little louder than a normal conversation volume. Is that right for this model? This is my first leslie and I have nothing to compare it to

[David Anderson]

Do you have a full 21H Leslie cabinet with the field-coil woofer and horn driver? It won't be quite as loud as a 122 or 147, but it should be reasonably loud.

[Jamfu]

Yes I have all the original parts except the cabinet. The guy I got it from left it in so.ewhere and termites destroyed it.. but all the internal were fine. Date code on the woofer is 41st week of 1954. I have other guitar amps that are 30 watts and a lot louder than this this thing. Just curious how loud this thing will get

[David Anderson]

The 21H amp is officially just a 20 Watt amp. In reality, you usually get a bit more, but not 30W. Also, the Leslie radiates sound in all directions, and it's long been known that that reduces its perceived loudness compared to a guitar amp, which is directional and which usually (due to the speakers chosen for guitar amps) has peak output around 2-4kHz where the human ear is very sensitive.

The only real way to test to see if an amp is being driven to maximum power is to bench-test it. Most professional techs have a dummy resistive load and check amps using the resistor, an oscilloscope, and a test tone generator. This is more complicated with the field-coil amps since the field-coil needs to be in-circuit for these tests. I'm guessing that running tests like this is currently beyond what you know how to do.

If you made no mistakes in rebuilding the amp and if everything else is set up correctly, then the question becomes: Are you getting enough drive signal from the organ to drive the Leslie amp to full output?

[Ted J]

I have a 21 H, It's pretty loud. I had trouble after recapping the amp with low signal level - I made a rookie mistake reconnecting the wires at the input, tying the two balanced signals together, once sorted it had full volume.

[Jamfu]

David. I have a roland vk-08 and am using a leslie 1122 kit to convert from 11 pins to 6. As far as drive signal goes. I was taking voltage with everything hooked up. Speakers, motors etc.. and the line viltage dropped to 80 volts out of the fuse to ground. I thought I was going crazy.. I measured voltage at the wall socket its 120vac. Voltage at the 6v6s was 50vdc were the circuit says it should be 330v.

A few things. I replaced 1 capacitor at a time I figured I'd get into trouble if I went nuts and cut them all out at once . What are the 3 plugs for on the top of the amp B B A ? I assume both Bs are for the speaker motors . But what's the 3rd for? Also when I got the amp home. It only had 1 rectifier tube In it, and the other tube socket was taped over with what looked like original 1950s tape. So it had lived its life with one rectifier tube. I cant think of why when both tube sockets are wired per the circuit.

my plan tonight is to fire it up and measure voltages at every interface and see what's what. The 80 volts really has me scratching my head . By the way . With the motors plugged in the current draw is enough to light to limiting light bright. I'm not totally confused yet but rapidly getting there. I'll have to try to make sense out of the voltages I get later tonight

[KC9UDX]

?

You need both tubes. It's supposed to be a full-wave rectifier and you're only running half-wave. Unless someone rewired the plates on the one remaining tube, which is a bad idea.

[Jamfu]

I was looking at the pictures I took of the rectifier circuit and someone had taken one of the tubes out of it.that begs a million more questions now.

[KC9UDX]

I wouldn't try to figure out why someone felt it necessary to undo the manufacturer's intent. It's easy enough to put it back to the way the schematic shows it.

[tpappano]

Maybe someone replaced the two 5Y3s with a single 5U4?

[KC9UDX]

If so, I hope they knew what they were doing. Two 5Y3s can conduct more current and better dissipate heat than a single 5U4.

[David Anderson]

Actually, Leslie did that themselves. Early 21H/44W amps use two 5Y3s, but later versions use a single 5U4GB.

I've noticed that these amps will wear out a single 5U4GB. It probably made sense on paper at the time, looking at the datasheets.

[David Anderson]

In the earlier versions of this amp, which yours appears to be, Leslie used two 5Y3 rectifier tubes, but each tube is wired as a single diode with the two plates wired together at the tube socket. As a pair, operating together, they form a full-wave rectifier.

It looks like someone rewired yours to use a single rectifier tube as a full-wave rectifier. A single 5U4GB should work, so that should not be the cause of low volume.

[Jamfu]

Yes you can see an old soldered connection at pins 6 an 4 in the rectifier circuit . I put the jumper wires back . It certainly helped the voltages some., but like you say no help with the volume. With the motors plugged in I'm getting 9vdc from pin 8 to ground . Not 19, . I started mapping out the voltages at every interface to try to find the issue. Are the voltages on the circuit with everything hooked up or just at idle no motors or speakers? I'm getting confused about this. Thanks again guys

[David Anderson]

Voltages are with the field-coil speaker plugged in. The motors operate off AC and are not involved with the audio circuit at all -- or shouldn't be.

Again, 99% of the time a newbie comes on here with a question of this nature, it's because they made a mistake somewhere. The problem is that the only person who's really in a position to find the mistake is the person who's asking the question, and they're not seeing it because they don't have the experience.

If I were you, I would take a break from it and then go back and methodically check everything you did against the schematic.

[Jamfu]

Yeah that's the case and what I plan to do. when I design my plan is always done before the execution . Total newbie to audio amps. I'll get it right, just have to go through the growing pains like every one does. And like you said the only way is to methodically go through everything.