too long strat 'clip'

[heisthl]

Here's one way to drive a relay with the filaments (from a Yamaha schematic)

[mat]

Hello there,

I finally got time to troubleshoot my amp. The result is that with the heater supply for th relays (2) disconnected the amp is somewhat noise free - little bit of hiss in there. I tried lots of things to get rid of the remaining hiss but did not succeed.

I tried the relays powering them with 9v battery. Worked like a charm and very low noise again. So I will buy a 6-9v transformer for the relay supply.

After few hours soldering/rewiring etc. I got nasty sizzle when turning (one tube) reverb pot. It does not give any reverb, only sizzle I have had earlier same kind of noise but it has faded away by itself ? I will try to cange the reverb tube. I measured the plate voltage and it was 470V The pot at zero there is no noise at all..

Any idea for the reverb problem ?

Thanks,

[Normster]

Anytime I have problems with a reverb circuit, the first thing I try is new cables. I learned that lesson the hard way after completely rebuilding the whole reverb section. So far I've had two sets of bad cables and each time the symptoms were different.

[glasman]

After few hours soldering/rewiring etc. I got nasty sizzle when turning (one tube) reverb pot. It does not give any reverb, only sizzle I have had earlier same kind of noise but it has faded away by itself ? I will try to cange the reverb tube. I measured the plate voltage and it was 470V The pot at zero there is no noise at all..

Any idea for the reverb problem ?

Thanks,

Questions .....

1. Are you using a dropping resistor before the reverb tranny?
It should be in the range of 27K to 75K. Add a .1uf cap between the
resistor and transformer junction to ground. As simple as it sounds it really improves the reverb.

Drive side Checks.

1. Make sure that the cathode connections are good. Check the tube connections, cathode resistor, cathode bypass cap and the associated ground. If the plate is floating at the supply the tube is not conducting and either the tube is smoked or the return path to ground is not good.

2. As Normster commented, check the cables. Given the conditions you mention I doubt this is the problem.

3. Is the the reverb tranny getting hot. Probably not given the 470 on the plate of the driver. But worth the check.

4. The cathode of the driver side will measure in the neighborhood of 4 to 7 volts to ground depending on the cathode resistor and the supply voltage.

Recovery side checks.

1. Plate voltage should be in the 200 +/- range.

2. Cathode voltage will be in the 1.5 to 2 volt range.

3. Simple check for recovery side. Attach RCA cable to reverb tank return jack on the chassis. Touch the center conductor, you should hear an AC hum as you turn up the reverb control. If so, the recovery is probably working.

Gary

[mat]

Thanks Normster and glasman

I will try as adviced on day after tomorrow and return with results.

[mat]

Funny thing, I changed the cable and now the noise is gone. But when I changed the old cable back it works also perfectly. I moved and twisted the old cable properly but no noise ?

1. Are you using a dropping resistor before the reverb tranny?
It should be in the range of 27K to 75K. Add a .1uf cap between the
resistor and transformer junction to ground. As simple as it sounds it really improves the reverb.

No, there is only the choke before the RT, as in : http://www.pichotel.com/pic/16028B31e/132360.jpg. I will add the resistor + cap later.

Drive side Checks.

1. Make sure that the cathode connections are good. Check the tube connections, cathode resistor, cathode bypass cap and the associated ground. If the plate is floating at the supply the tube is not conducting and either the tube is smoked or the return path to ground is not good.

cathode connections checked - ok. First to ground 0.8k (0.68uF in circuit), second 2.17k (2.87uF).

2. As Normster commented, check the cables. Given the conditions you mention I doubt this is the problem.

That doesnt seem to be the (now absent) problem.

3. Is the the reverb tranny getting hot. Probably not given the 470 on the plate of the driver. But worth the check.

It does not eaven get warm.

4. The cathode of the driver side will measure in the neighborhood of 4 to 7 volts to ground depending on the cathode resistor and the supply voltage.

I get 3.17V on the first cathode.

Recovery side checks.

1. Plate voltage should be in the 200 +/- range.

2. Cathode voltage will be in the 1.5 to 2 volt range.

1. 477V and 198.8V

2. 1.8V

3. Simple check for recovery side. Attach RCA cable to reverb tank return jack on the chassis. Touch the center conductor, you should hear an AC hum as you turn up the reverb control. If so, the recovery is probably working.

Yes, it does exactly as You suggested.

[glasman]

Funny thing, I changed the cable and now the noise is gone. But when I changed the old cable back it works also perfectly. I moved and twisted the old cable properly but no noise ?

1. Are you using a dropping resistor before the reverb tranny?
It should be in the range of 27K to 75K. Add a .1uf cap between the
resistor and transformer junction to ground. As simple as it sounds it really improves the reverb.

No, there is only the choke before the RT, as in : http://www.pichotel.com/pic/16028B31e/132360.jpg. I will add the resistor + cap later.

Drive side Checks.

1. Make sure that the cathode connections are good. Check the tube connections, cathode resistor, cathode bypass cap and the associated ground. If the plate is floating at the supply the tube is not conducting and either the tube is smoked or the return path to ground is not good.

cathode connections checked - ok. First to ground 0.8k (0.68uF in circuit), second 2.17k (2.87uF).

2. As Normster commented, check the cables. Given the conditions you mention I doubt this is the problem.

That doesnt seem to be the (now absent) problem.

3. Is the the reverb tranny getting hot. Probably not given the 470 on the plate of the driver. But worth the check.

It does not eaven get warm.

4. The cathode of the driver side will measure in the neighborhood of 4 to 7 volts to ground depending on the cathode resistor and the supply voltage.

I get 3.17V on the first cathode.

Recovery side checks.

1. Plate voltage should be in the 200 +/- range.

2. Cathode voltage will be in the 1.5 to 2 volt range.

1. 477V and 198.8V

2. 1.8V

3. Simple check for recovery side. Attach RCA cable to reverb tank return jack on the chassis. Touch the center conductor, you should hear an AC hum as you turn up the reverb control. If so, the recovery is probably working.

Yes, it does exactly as You suggested.

Things appear close and it sounds like the recovery side is working.

Probably a problem on the drive side.

Here is a simple check, connect a small speaker (4 or 8 ohms) to the output side of the reverb transformer. If the driver is working correctly you should be able to hear a little sound thru the speaker. If not you have a pretty good place to start looking.

If you have a scope, try measuring the drive side plate with respect to ground and see if have a signal on the plate. Also make sure that the 1M on the grid is grounded otherwise this stage will not work.

I will comment (I learned this the hard way). Give your setup, you have (or should have) about 473 volts on the plate of the drive side. With a cathode voltage of 3.17 volts you have a plate curernt of

3.17 / 820 = 0.0038 mA and a plate dissipation of 1.82W. The maximum plate voltage and maximum plate dissipation are both being exceeded. I would imagine the tube is a tad warm.

I would seriously suggest knocking the voltage down a bit. Given 4ma on the drive side and about .82mA on the recovery side I would suggest shooting for, say 350 on the supply side by insertings a (477-350) / .00482 = 27K resistor (even 47K) 2 watt resistor with a 10 to 22uf filter cap on the reverb side.

Gary

[mat]

Gary, do You mean 27k-47k in parallel with 10uF-22uF from B2 to RT blue wire (on the layout) ? . . .

[glasman]

Gary, do You mean 27k-47k in parallel with 10uF-22uF from B2 to RT blue wire (on the layout) ? . . .

The 27K to 47K should be ibetween the power supply and the blue wire of the reverb transformer. The 10/20uf cap should be from the junction of the resistor and transformer to ground making it a filter cap.

Gary

[mat]

Gary, do You mean 27k-47k in parallel with 10uF-22uF from B2 to RT blue wire (on the layout) ? . . .

The 27K to 47K should be ibetween the power supply and the blue wire of the reverb transformer. The 10/20uf cap should be from the junction of the resistor and transformer to ground making it a filter cap.

Gary

Gary,

I have the last filter section on my powerboard free (B6 on the layout). It contains two 47uF in series with 330k's accross both of them. Any use of them in this situation, or should I just did what You said earlier ?

The design uses also B5 to feed both the reverb tube plate 2 and V1 plates. Would it be better to feed the reverb plate 2 from B6 and V1 plates from B5 ?

Thanks

[mat]

Gary,

I did put in a 39K/3W from B2 to the transformer (+ 22uF/450V to ground from their junction).

I have got something wrong with my amp because the sound is not right right now. The sound is farting and feels like heavily unbiased (tried with pair of 6L6's-40mV and 6V6's-25mV).

I measured the voltages and V2b was only 86-90V (with two different tubes). Everything else seems to be in range. (V1 186V-193V, V2 193V-).

What might cause the V2b to be so low? The B4 (feeding the V2) is 342V.

[glasman]

Gary,

I did put in a 39K/3W from B2 to the transformer (+ 22uF/450V to ground from their junction).

I have got something wrong with my amp because the sound is not right right now. The sound is farting and feels like heavily unbiased (tried with pair of 6L6's-40mV and 6V6's-25mV).

I measured the voltages and V2b was only 86-90V (with two different tubes). Everything else seems to be in range. (V1 186V-193V, V2 193V-).

What might cause the V2b to be so low? The B4 (feeding the V2) is 342V.

The first step is to undo the last step if you are sure things were ok to begin with.

The addition of a series resistor and 22uf to ground (unless the cap is shorted) should not affect your V2b voltages.


As your V2a voltage is ok. I would assume a problem around the grid of V2b, maybe a leaky cap from V2a. Or that the cathode is sitting at ground and the tube is running full tilt on boogie. Check your cathode voltage, should be about 1.6 yo 2 volts. Higher that 2.5 is not good and neither is 0.

Gary

[mat]

The first step is to undo the last step if you are sure things were ok to begin with.

I did that but the problem remains.

The addition of a series resistor and 22uf to ground (unless the cap is shorted) should not affect your V2b voltages.

The cap is new, I might try to disconnect it to measure the V2b again, but as You said this is not very likely the problem.

As your V2a voltage is ok. I would assume a problem around the grid of V2b, maybe a leaky cap from V2a. Or that the cathode is sitting at ground and the tube is running full tilt on boogie. Check your cathode voltage, should be about 1.6 yo 2 volts. Higher that 2.5 is not good and neither is 0.

I'll do the measurements first thing at tomorrow.

[mat]

The V2b cathode is 3.56V ! Should I change the .01 connected to V2a plate ? Or the cathode caps ?

The voltages are:

B+1 = 467
B+2 = 465
B+3 = 443
B+4 = 325
B+5 = 306

V1 - pin1 = 194, pin3 = 1.64, pin6 = 205, pin8 = 1.46
V2 - pin1 = 216, pin3 = 1.62, pin6 = 86.7, pin8 = 3.56
V4 (reverb) - pin1 = 350, pin3 = 2.37, pin6 = 186, pin8 = 1.74
V3 (PI) - pin1 = 330, pin2 = 40, pin3 = 67.5, pin6 = 342

edit: I changed the cap from V2a plate to a fresh one but it did not affect to the voltage of the V2b...

[tonelab2]

It may sound silly but have tried a new tube in V2? Had a similar problem with a bad batch of EH tubes.