Paramour 1 Troubleshooting

[jeff g]

Hi all.  I'm a lapsed member who built Paramour 1s a few (7, 8?) years ago and have been enjoying them since.  Recently one channel crapped out and I'm trying to troubleshoot.  I'm having trouble getting started as I lost my manual.  Eileen was kind enough to send the Paramour 2 version, but it's different enough that it's confusing me.

So, would anyone have a scan of the labelled layout and resistance / voltage values for the Paramour 1?

Also, any tips for where to start?  While playing, the amp made a scratchy / fizzly sound losing volume and then cutting out entirely.  I thought it might be a tube, but when I went to switch it the fuse was blown.

thanks in advance
Jeff

[Doc B.]

First step is to look for anything under the chassis that might have moved and shorted against another part. Check the rectifier diodes with an ohmmeter to see if they measure blown (shorted out, i.e., very low resistance like under 100 ohms). That would be an indication of a short somewhere downstream that pulled more current than they can handle. Next you might want to try different tubes to see if one has gone bad. If they are OK, the next step might be to replace the filter caps. 8 years of operation is fairly long for a cap and could well be past the rated operational lifetime if the amp has had a lot of use. A failing filter cap could cause the B+ voltage to drop and eventually draw enough current to take out the fuse. One can also disconnect the amp circuit from the power supply circuit and see if the power supply will hold without blowing the fuse. That would indicate that the problem is in the amp circuit and not the power supply.

[jeff g]

Thanks Doc and Grainger.

I managed to find my manual so I'm ok on that front (but time for a house cleanup I think).

I'll try Doc's suggestions, check resistances/ voltages and post again.

Funny, I wouldn't have thought the caps would be gone already.  The amps haven't really been heavily used and I've got receivers from the 70s which I don't think have ever been serviced - but maybe their performance isn't as good as it could be.

[Grainger49]

Electrolytic caps have a finite life from manufacture.  The electrolyte drys up over time.  Amps and receivers from the 70s are in need of "recapping."  That can be expensive so you might select the critical caps.  Power supplies need fresh caps.  Any electrolytic in the audio path should be exchanged, with a film if possible.

[Doc B.]

Caps come from the manufacturer with a lifetime rating that is based upon operating temp. That's not to say that very many users heed it. As an example the Panasonic TS-HB series is rated 3000 hours at 105C. That lifetime can be extended somewhat if run at a lower temp. But it can get pretty warm in a tube amp chassis. The ED series is rated at more like 8000-10000 hours at 105C.

I'd be inclined to check the other stuff before replacing caps just in case it's something else that is causing the problem. But it's not a bad idea to replace electrolytic power supply caps on gear that has some time on it. We have been sent a few older amps to go through lately, and we replaced the filter caps in them before sending them back.

[jeff g]

ok, no visible shorts and diodes are ok.  not sure how to disconnect the amp circuit from the power supply circuit, so I haven't done that.

all resistances were ok, so I tried the smoke test - failed.  there was a little bit of smoke around T1, not sure what exactly.  After that, the fuse was blown and resistances at T1 and T2 were low (T1 = 178 should be 215-240; was 221 prior to smoke check / T2= 83, should be 215-240; was 210 prior to smoke check).

all other resistance values were ok and diodes are still ok

resoldered a few terminals, but I'm not sure which need to be redone, if any.

where to from here?

[Grainger49]

Jeff,

The wires going out of T15 are the ones that feeds power out to the tubes.  They should go to the plate choke, and to either a C4S board or T19 feeding the driver tube.  So you will have to lift both.

Like Doc says, this splits the amp to power supply and audio circuits.  

If the fuse blows you have isolated it to the two diodes, two caps, a bleeder resistor and a PS resistor (choke if you upgraded your iron).

[jeff g]

so, just disconnect the 47uf cap and 15k resistor, leaving all else as is?

[Grainger49]

Jeff,

I only checked my schematic showing the second 47uF cap connecting to the plate choke, and to either a C4S board or T19 feeding the driver tube.  I'm not sure how it is all connected.  I should check the finished picture.  

The 47uF cap should stay as it is.  The voltage going out from there is what you want to open.

Do you have C4S and/or iron upgrades?

Edit: I checked the picture and there are two wires you need to lift to take the load off of the power supply.  The first one goes to the plate choke mounted on top of the top plate.  The other one goes to pin 1 of the driver 12AT7.  You can lift the one to the 12AT7 at the tube socket and wrap it with electrical tape.  I'm not quite clear where the wire from the plate choke is.  Most likely under the capacitor at T15.

[Grainger49]

And more... I see no 15k resistor on the schematic.  But the Paramour has gone through all kinds of changes.  The power supply includes a 270k bleeder and a 270 ohm resistor between the two caps.  None of this should be disconnected if you want to test the power supply.

The two windings for the heaters will still operate so the tubes should glow and get warm if you leave it on long enough.

Good luck!

[jeff g]

my T15 has 4 connections

1.  one of the twisted pair from the transformer (I assume this is the choke?) - the other half goes to the 2a3
2.  270 ohm 5w resistor between the caps
3.  47uf cap
4.  15k 3w wirewound resistor to the C4S (terminal strip)


so, I should lift the 15k resistor and the half of the twisted pair at T15, correct?

[Grainger49]

1) is as you assume, the choke is in between the B+ and the 2A3 plate
2) stays
3) stays
4) that is one

So, yes open the two you have called out. 

I don't remember or have documented the 15k resistor.  That is odd.  I have the C4S and it is simply wired to terminal 15.  Are you using a different driver tube than the 12AT7?

[jeff g]

ok, i'll give it a try within the next few days.

my c4s was stock and the 15k resistor is listed in that manual - I'm using a 12at7

even if I can figure this out, I'm planning on replacing the caps - might do the foreplay while I'm at it as that's even older

thanks again

[Grainger49]

Jeff,

It is no surprise to folks here that I'm a capacitor junkie.  I replaced my power supply caps with 47uF PP film caps.  I upgraded the iron with MQ iron and changed the  Parafeed cap with an Obbligato 10uF Film and Oil.  The only cap that hasn't been changed is the cathode bypass cap.  I should improve that one.

I bought my Paramours when Doc announced the sale of the last 4 pair of Paramours before the Paramour II release.  So it is the latest production possible.  I bet you have a different transformer than I do.

[jeff g]

I disconnected the 15k resistor and choke wire at T15 and the fuse still blows.  So I guess I should replace the 2 diodes, 2 47 uf caps, and resistors, correct?   Is the 270 ohm 5w the power supply resistor?  Anything else to replace?