Plush tube amp - please help

[GlennW]

I have a Plush Royal 1060-S bass amp (ebay) and it doesn't come on. After taking a peek inside a couple things don't look too sporty.

I'll try to explain the pictures now.

The first two pics will be of what's there now. Someone spliced in a cap can in place of what I think should be a 100 MFD/350 VDC power supply cap. The diodes on the left cause the DMM to make a noise; the one on the right checks ok, but looks like it's cracked. The pointy diode? on the left is disconnected on one end where it looks like a few leads were soldered together. I have now idea how any of this coincides with the schematic.

I have a schematic which will be shown in the following post, but I can't read it.

Since it's hard to see the details in the pics, I'll also include a drawing of how stuff is connected now. I've labeled the solder terminals on the left 1-5 (top to bottom) and the terminals on the right A-E top to bottom to make it easy to understand (for me).

I've also included any markings on the pieces I could read.
Both of the red highlighted things are marked MB, PTC, 205.
The pointy black thing on the left is marked F, 871; and the one on the right has some of the writting worn off, but might be HC or RC, 69.

If you can look at the schematic and tell me what to do I'll be most greatful; like "100MFD/350VDC cap with the + lead to 1 and the other lead to A" so I can understand it.

I also need the specs on the diodes if anyone can make a good recommendation.
Thanks.

[52 Bill]

Originally Posted by GlennW

I have a Plush Royal 1060-S bass amp (ebay) and it doesn't come on. After taking a peek inside a couple things don't look too sporty.

If it does not power up, (no pilot light, tube filaments don't light, etc.) check the fuse, power switch and the ac cord and plug. If all of these are ok then check the power transformer primary for continuity with your multimeter.

Originally Posted by GlennW

The first two pics will be of what's there now. Someone spliced in a cap can in place of what I think should be a 100 MFD/350 VDC power supply cap.

Yes, that is what it looks like to me too. I would suggest replacing both when you get the amp up and running.

Originally Posted by GlennW

I also need the specs on the diodes if anyone can make a good recommendation.

1N4007 will be a good choice here. It looks like the larger diode is original to the amp and was not removed when the amp was last worked on.

[GlennW]

Thanks a lot, Bill.

I took some close-ups of the diodes and tested them with a DMM after snipping one lead.

The big pointy one by itself (between terminals B and E on my hand drawn diagram) read "1" with the red probe on the pointy end, and read "474" with the black probe on the pointy end. It's my understanding that means it's ok, but I'll replace it anyway.

The little one by itself (between terminals 2 and 4) read "1" with the red probe at the end with the line (towards terminal 4), and read "552" with the black probe on the end with the line.

Both of the other two diodes, one large and one small (between terminals 5 and 4) made the DMM buzz with the probes connected both ways. I think that means they're shorted out.

I'm going to replace all four diodes and the two 100MFD/350VDC caps, and add a 3-prong cord.

I'll order two 1N4007 diodes for the little ones. Is there a Mouser part number you'd recommend?

How about the big diodes with the pointy end? Does the 474 reading shed any light on what to get?

I'm a little suspicious of the PT since both of the shorted diodes are connected to the same red wire on terminal 5. Maybe it's a coincidence, maybe not. I'll replace the diodes and two caps first and see what happens.

I'm pretty clueless about this stuff.

Thanks.

[52 Bill]

Originally Posted by GlennW

The big pointy one by itself (between terminals B and E on my hand drawn diagram) read "1" with the red probe on the pointy end, and read "474" with the black probe on the pointy end. It's my understanding that means it's ok, but I'll replace it anyway.

I'm not sure how your meter works, but when you have the leads unhooked to anything does the display read "1"? If it does, then the diode is ok. The "474" would indicate the voltage at which the diode junction conducts, 0.474 volts dc.

Originally Posted by GlennW

Both of the other two diodes, one large and one small (between terminals 5 and 4) made the DMM buzz with the probes connected both ways. I think that means they're shorted out.

Try removing one of the two diodes by clipping one lead. One may be shorted, and the other one may be ok.

Originally Posted by GlennW

I'm going to replace all four diodes and the two 100MFD/350VDC caps, and add a 3-prong cord. How about the big diodes with the pointy end? Does the 474 reading shed any light on what to get?

There should only be 3 diodes total in the amp. Whoever worked on the amp before didn't do too good of a job. There should be one diode from 2-4 and one diode from 5-4 (not 2). These are the B+ (high voltage) supply diodes. If you look at the schematic, these are the 2 diodes pointed upwards that connect to the two 100/350 caps.

The diode that goes from e-b is the bias (negative voltage) supply diode.

Any of the three of the diodes can be replaced with a 1N4007. If you want to use something with a higher current rating you can do that as well.

Originally Posted by GlennW

I'm a little suspicious of the PT since both of the shorted diodes are connected to the same red wire on terminal 5. Maybe it's a coincidence, maybe not.

As I noted above, when two diodes are paralleled if one shorts, they will both test bad.

I would suggest removing all traces of what the last tech did, as the work was not quite up to par.

Is the amp blowing fuses? If not what kind of ac readings are you getting from the transformer secondaries?

[GlennW]

Thanks, Bill.

I'm going to remove the four diodes and two PS caps and replace them with three diodes and two PS caps, Mouser numbers 625-1N4007GP-ES/54 diodes and 75-TVA1620 caps. I don't think the guy messed with anything else, I hope not. I might try to add a couple of resistors to make it easy to balance the bias.

I don't think the amp was blowing fuses. I bought it a few years ago off ebay and I think it worked at that time. I really don't remember, but I'm pretty sure if it didn't work I'd remember getting mad that it didn't; never used it since then. I listed it on ebay a few months ago (thinking that it worked) and discovered it didn't; the pilot light didn't come on and the tubes didn't light up. Then I put it away until this past Sunday.

I've taken no ac readings at all.

I'll add a 3-prong cord, replace the diodes and caps, and post the results; it'll probably be a week or so.

Thanks again for the advice, I really appreciate it.