Where to find 6000uF 50V replacement cap cans??

[g1]

As to your question about the diode check on the TIP32, was it the one shown as Q10 in the diagram you posted?
R47 and R41 form a 702R resistor from emitter to base, so that parallel resistance will make the diode check read lower.

[RG100ESROX]

Thanks for the reply.

I have some random questions...

1) Can I power up the amp without any of the power transistors installed to take voltage readings...?

Answer 1):

2) Does this amp require a speaker to be plugged into it, or must a dummy load be used?

Answer 2):

3) Can I plug headphones into the direct out (DI) jack WITHOUT a speaker plugged in?? Or, must there be a dummy load attached in conjunction with the headphones?

Answer 3):

4) Can the 120 VAC accessory outlet on the rear panel be wired at the power switch so that it can be controlled with the switch as well as the amp?

Answer 4):

5) Any advantage to using an attenuator with this amp. (I've been a tube amp guy for so long I don't know the answer to this.)

6) Dumb question, but...should I be getting a resistance reading between the + and - of the input jacks? I'm assuming so, but .4 ohms is kind of like a short, no? I'm getting about .4 ohms on the Hi input and 137K on the Lo input.

Answer 6):

7) Why am I getting a reading in both directions on a few of the diodes on the board?? Shouldn't I see an open in one direction??

Answer 7):


Thanks in advance to whoever replies.

[g1]

1) Can I power up the amp without any of the power transistors installed to take voltage readings...?

Answer 1):  Yes, I don't see a problem with that in this circuit.

2) Does this amp require a speaker to be plugged into it, or must a dummy load be used?

Answer 2):  No speaker or load required

3) Can I plug headphones into the direct out (DI) jack WITHOUT a speaker plugged in?? Or, must there be a dummy load attached in conjunction with the headphones?

Answer 3): no load required

4) Can the 120 VAC accessory outlet on the rear panel be wired at the power switch so that it can be controlled with the switch as well as the amp?

Answer 4):Yes, but the extra current will be through the amp's circuit breaker, so depends on what you want to plug in there

5) Any advantage to using an attenuator with this amp. (I've been a tube amp guy for so long I don't know the answer to this.)
Answer 5) can't see any advantage to this, will just make the amp run hotter which is worse for it

6) Dumb question, but...should I be getting a resistance reading between the + and - of the input jacks? I'm assuming so, but .4 ohms is kind of like a short, no? I'm getting about .4 ohms on the Hi input and 137K on the Lo input.

Answer 6):  The input jack's switch contact shorts it out when nothing is plugged in, to avoid hum and noise

7) Why am I getting a reading in both directions on a few of the diodes on the board?? Shouldn't I see an open in one direction??

Answer 7): parallel resistance in the circuit may give a reading in reverse-bias direction, and lower than normal reading in forward biased direction.  When in doubt, disconnect one end of diode from the circuit.

[RG100ESROX]

Thank you for taking the time to response to my questions. I really appreciate it.

So, "No load." How easy is that??

And with respect to the input jacks. They're not 'Cliff' jacks.(see photo)
(I am mistaken. They ARE like cliff jacks. I just couldn't tell until got in there.)

Also, without the power transistors in, my channel LEDs don't work. Just want to be sure this is to be expected??

I'm also getting some higher than normal voltages around the bias pot without the power transistors. Is this also to be expected??

[RG100ESROX]

Anyone care to trace the signal path from the input jacks all the way to the output jacks?? I'd love to have this for my records.

[RG100ESROX]

Yet another stupid question..

Can someone tell me what this is, and what its purpose is???

I've never seen anything like it before.

[Loudthud]

Looks like a thermister, marked TRM on the schematic.

[RG100ESROX]

Looks like a thermister, marked TRM on the schematic.

I'm guessing it's used to monitor the temp of the power transistors in case they over-heat? In which case if breaks the circuit??

[Loudthud]

Breaking the circuit would blow the Mains fuse or trip the circuit breaker. Thermisters and diodes are used to keep the bias current of the output (and driver) transistors the same as they heat up.

[RG100ESROX]

Breaking the circuit would blow the Mains fuse or trip the circuit breaker. Thermisters and diodes are used to keep the bias current of the output (and driver) transistors the same as they heat up.

Thanks for the clarification.

Any idea what its value is?

[Loudthud]

These things are very difficult to replace, you'll need to get the exact part number and vendor from Randall, or beg them to sell you the part. Say a little prayer that the part isn't bad.

[RG100ESROX]

These things are very difficult to replace, you'll need to get the exact part number and vendor from Randall, or beg them to sell you the part. Say a little prayer that the part isn't bad.

Any way that you know of to test it??

Do we even know it's value?

[g1]

Also, without the power transistors in, my channel LEDs don't work. Just want to be sure this is to be expected??

I'm also getting some higher than normal voltages around the bias pot without the power transistors. Is this also to be expected??

Neither of these issues make sense to me.  With power transistors removed, main supply voltages may increase a bit but not much.  That should not affect the channel lights or the bias circuit.

[RG100ESROX]

Also, without the power transistors in, my channel LEDs don't work. Just want to be sure this is to be expected??

I'm also getting some higher than normal voltages around the bias pot without the power transistors. Is this also to be expected??

Neither of these issues make sense to me.  With power transistors removed, main supply voltages may increase a bit but not much.  That should not affect the channel lights or the bias circuit.

Yet again I am incorrect. The LEDs do work. I used a 3v watch battery to confirm this.

Sorry for creating an unnecessary reply. )-8

[RG100ESROX]

Just so we're all on the same page..

The reason for all of my questions now is....I did a VERY stupid thing the other day while tying to get a sine wave and check the bias reading at the sametime.

I VERY stupidly grounded my O-Scope to the Hi input jack grounding lug. And...now the amp does not work. All I get is a hum/buzz out of the speaker.

In my defence, I did not see that the input jacks were indeed like cliff jacks (still, no excuse. I knew better than that.) Stupid, stupid, stupid.

Well, now I'm paying the price with unnecessary troubleshooting. Live and learn.

So, I have replaced all of the power transistors (which turned out to (all) be okay anyway.) The TIP 31C and TIP 32C's and the OpAmp (I had these anyway.)

I have some 1N5484's coming and they'll be here on Monday.

I'm thinking that I at the very least blew the first if not first few transistors in the preamp stage. However, I'm just going to replace them all. There's a chance I could have blown the first few electrolytics as well, BUT...none of the caps or resistors look any worse for the wear. I did measure the resistance of all of the resistors in the preamp section, and they all checked out okay.)

My worst fear however, is the thermistor. That is the ONLY area I caught a glimpse of smoke at the time of my IDIOTIC mistake.

I have contacted Randall (I'm not holding my breath that they'll be able to answer my query) in an attempt to find out what the value is of the thermistor. If I measure it I get a resistance of 67R +/-. But, we don't know what it SHOULD be..

So, that's where I'm at now. When all I wanted to do was find out why the amp was sounding so round and flubby. Geeeeeeez.

Just another day in my world.