Help with 100 watt Marshall 2210 PT

[chabby-ao]

I'm having trouble with a Marsall 2210 and getting various readings that are baffling me. I finally disconnected the high voltage AC wires from the stand by switch to take a voltage measurment and get (rounded) 118 VAC (Blue) and 188 VAC (Grey). This seems very low to me as I expected these readings to be around 700 VAC. What's going on?

Thanks

[JayB]

I'm having trouble with a Marsall 2210 and getting various readings that are baffling me. I finally disconnected the high voltage AC wires from the stand by switch to take a voltage measurment and get (rounded) 118 VAC (Blue) and 188 VAC (Grey). This seems very low to me as I expected these readings to be around 700 VAC. What's going on?

Thanks

Looks like one side of that winding is shorted out. They both should be fairly close to the same reading. That amp uses a full wave bridge rectifier, a set of 4 diodes. I can't remember what the proper voltage on that amp but 175VAC should be on each leg of that winding for 350VAC total. That would get you around 495 - 500 DC unloaded.

Next guess is why and I'm betting one of those diodes on the grounded side is shot.

[sluckey]

I'm having trouble with a Marsall 2210 and getting various readings that are baffling me. I finally disconnected the high voltage AC wires from the stand by switch to take a voltage measurment and get (rounded) 118 VAC (Blue) and 188 VAC (Grey). This seems very low to me as I expected these readings to be around 700 VAC. What's going on?

Chabby, since this PT uses a bridge rectifier and there is no center tap connected to chassis on the high voltage winding,  you must measure the voltage BETWEEN the blue and grey leads, rather than from chassis to each lead.

[chabby-ao]

Okay, I'll measure voltage between them and also check diodes too.
Can a bad diode short out the PT there?

Keep in mind I'm measuring the voltage without the HV lines connected to the rectifier. But I'll try and see why they aren't identical.

[eleventeen]

What are you using as a reference when obtaining those voltage values?

Though it is unused in the actual circuit; if you can get to the CT wire without too much hassle, 2 measurements from the outer HVAC leads to the CT would be useful. Should be very close to equal. If you can't easily get to the CT wire, then measure (carefully) across the entire HV winding. If you pull the B+ fuse, the B+ volts available at the + terminals of the 50/50 electrolytic caps should be about 1.4x times the AC reading you obtain across the full HV winding. Do the math first on this and do not make this measurement if that 1.4x figure will exceed the ratings on those caps!

And...never wanting to overlook the obvious...the AC mains switch didn't slip over to the 240 VAC position did it? LOL.

[chabby-ao]

No - I checked it and it's at the 120 VAC click.

[chabby-ao]

Also - looking at this schematic I can't see where 2 different grounds go.
There's one at the corner of the PCB board and one at the ground side of the rectifier. See this Plan: http://www.amparchives.com/album/Marshall/Schematics%20&%20Layouts/Marshall%20Amp%20Schematics/JCM%20800%20Series/2210%20100W%20Master%20Volume%20Split%20Channel/slides/2210pwrm.html

Then look at this picture: http://www.amparchives.com/album/Marshall/JCM%20800%20Series/2210%20JCM%20800%20MV%20Split%20Channel%20100W/87%202210%20JCM%20800%20MV%20Split%20Channel%20100W%20SN%20SAV24088/slides/554136987_c9d584c013_b.html

I can't tell from either one where those two bacl ground wires go - oh I can make an assumption sure, but it almost looks from the picture like this guy has the 2 grounds both going to the ground terminal of the cap partially hidden underneath the board. That doesn't make sense to me.

{EDIT-- space before URL links --PRR}

[sluckey]

That's probably exactly where they go and that would be correct. Did you measure the voltage as I suggested? What problem are you chasing in this amp? Are you experienced?

[chabby-ao]

I am experienced...or so I thought. Every now and then I get a stinker usually in the form of a new version of a make or model I am familiar with case in point: this 2210. I have worked fine on JCM 800's and 1959's etc.

This one came to me in a bit of a mess without many connections.
Right now the amp hums even before the standby is taken off, and should be quiet then. I've got either some fundamental problems with the way I've hoked up the power to preamp sections including the 3 fitler caps possibly, though I know I'm close. It definitely matters which HV lines from the PT go to which diodes in the full bridge. And of course all wires to filters such as OT/CT - fuse and post rectifer to fuse andchoke etc. This amp is just enough different that I'm confused on things I thought I knew and now I feel like I know nothing.

There are no layouts anywhere on this model to even get an idea other than from photos which is really hard way to go. I'm can read schematics but sometimes have problems if things aren't spelled out or I'm building to a schematic without ever seeing the components hooked up before like with this amp. But in terms of this hum as soon as I turn on the power switch, I have never seen that before.....after the standby is put on , sure you expect to hear a hum, but not before.

[sluckey]

Right now the amp hums even before the standby is taken off, and should be quiet then.

Does the hum come from the speaker or the chassis?

[eleventeen]

Does the hum come from the speaker or the chassis?

For the amp to hum in standby  it would seem like the ground connection where the bias supply is grounded is somehow compromised.

[VMS]

There seems to be two versions of 2210.

Early (82):

http://www.el34world.com/charts/Schematics/Marshall_REVERB_2210-HEAD_4211-COMBO.pdf

and late (87-88):

http://www.ampwares.com/schematics/marshall/jcm800_splitch_100w_2210.pdf

[chabby-ao]

Right now the amp hums even before the standby is taken off, and should be quiet then.

Does the hum come from the speaker or the chassis?

Sorry for the delay, I had to go on a parts run - it hums through the speaker which is really, really a first for me on power up with a standby on stanby

[chabby-ao]

There seems to be two versions of 2210.

Early (82):

http://www.el34world.com/charts/Schematics/Marshall_REVERB_2210-HEAD_4211-COMBO.pdf

and late (87-88):

http://www.ampwares.com/schematics/marshall/jcm800_splitch_100w_2210.pdf

Mine is the later one and is a 100 Watt head I could tell at first glance as this one has the lower value fuses.

I've noe double checked everything to the schematic and now will take a bias voltage reading. All I did once I got the amp was re-capp the main filters and the preamp board. I used good quality F&T caps on filters and sozos on preamp board. Since so many things weren't hooked up when I got it I've had to follow the schematic. Ever since then my confidence has kind of gone out the window but my hunch is it's partly because I took it for granted everything else worked - I should have known way better than that! Now if it doesn't work shortly my guess is it's a combination of failed components such as biaas winding, PT or even OT problems. I may have to go back to ground zero and repower the damn thing, I hope not. At this point I just can't see what I could have done wrong on the hook up. Done continuity checks etc. Double and triple checked work to the point I'm starting to doubt even what I do know.

Okay I powered up to take a bias winding voltage and get 35.86 VAC (44.80 VDC) right at the post where the bias winding hits the preamp board. I'll take a a bias reading at the pins too....it reads:-42.10 VDC but I'm still getting a hum through the speakers...........what can that be??? I'm afraid to turn on the standby until that is resolved.

[chabby-ao]

Took a reading at the diode behind the bias caps and get -54.2 VDC and -42.1 at the pin.

[chabby-ao]

Okay the last things I have any doubt on (I hope) is this: Okay from the end of the B+ fuse I know that red wire goes to the OTCT terminal on the board.
Does the other terminal on the B+ fuse go to the far end of R58 which I believe is a 10K Resistor? Then does the red wire leading from the filter cap right underneath the fuses go to the next filter cap?

Because before I had those reversed in other words I had the far end of R58 going to the filter cap under the fuses and the inside fuse terminal going to that first cap (closest to the standby switch). I think that was wrong, but need to double check with you better schematic readers.

[chabby-ao]

Oaky I got everything hooked up properly and it's blowing the 1A B+ or HT Fuse. I'm at a loss but all I can think of is that the OT is shorted out as I don't know what else could be making this happen.

I guess I'll have to take it out and rigorously test it to see if it's the OT. Nothing else makes sense.

[VMS]

Can you post some pictures of your amp?

Also, did the amp work before the cap job and have you measured the B+ DC voltage?

[chabby-ao]

I'll try and post some pix - no the amp didn't work but wasn't sure exactly why - thought it was due to spent main filters possibly.
Also had a funky mod I still don't understand. Looks maybe like someone tried to add more gain to the master maybe.

The final reading I got at the rectifier was 387.0 VDC.
But for some reason it's blowing the B+ 1A fuse. when the standby is pushed on. I have NEVER had so much trouble with figuring out hook ups. But this thing has a few different aspects that are throwing me off for some reason - or not, and it's got nothing to do with my hook-up and more to do with either a shorted OT or PT winding maybe.
But nothing is obvious on initial OHM readings from Primary to secondary and all to ground. Crazy!

It's internals look exactly like the picture of the 2210 I posted. Thats why I just need to know where the red wires you see in that picture run. Starting from each leg of the B+ fuse and the filter caps and board. I've got the OT/CT Choke/CT and a red wire running to the end of the Fuse as I know should be correct. What I'm iffy on is where the inside fuse terminal red wire should first connect to - right now I've got it going to the filter cap next to the one 1/2 wat under the board. The other red wire I have running from the filtyer cap right under the fuses to and feeding the PI. Is this wrong?

[chabby-ao]

I'm wondering if maybe instead of the above I should have the red wire running from the end of the B+ fuse to the filter cap next to the one 1/2 way under the pCB board and the inside terminal of the B+ fuse runnign to the PI which is exactly in reverse of the way I have them now. Other than that, I'm confused. If that could just be cleared up it would help me alot by deducing several things at once, it will answer more of my questions just in and of itself.

[sluckey]

Trying to look at a few pics of that amp is an extremely hard way to tell how to reconnect those wires. You really need to just wire it according to the schematic.

[chabby-ao]

I agree - so this should solve the whole deal - tell me if I read it right: I see the B+ off the rectifier wired to the filter cap then the filter cap wired to the B+ fuse the the other side of the fuse wired to the OT/CT Terminal along with the choke CT.

I know that's correct if I'm reading it right. THe only thig I wasnt to confirm is that the the first fuse connection I mention should go to the inside fuse terminal or the one on the end? My guess is it goes to the terminal on the inside of the fuse then the end of the fuse runs to OT/CT and choke Right? I think I had these reversed with the cap hooked to the inside of the fuse and the OT/CT and the cap from the rectifier hooked to the end of the fuse.

Please tell me this is it-lol!

[sluckey]

From an operational standpoint it doesn't matter which way you connect the fuse. From a SAFETY standpoint, connect the source voltage to the end of the fuseholder. Specifically, in your case, connect the cathodes of D9/D11 and the positive terminals of C49 to the end of the fuseholder. Connect the choke and the OT center tap to the side of the fuseholder.

[VMS]

I see that you guys already solved this while I was drawing my picture, but I post it anyway.

Here's how I see the amp is wired. What do you guys think?

[chabby-ao]

Okay - done, thank you.

Now I just have to figure out why I'm blowing that fuse when I hit the standby.
Everything seems right from a hook up stand point with that last confirmation.
I'll pull tubes and see if it still blows.

Okay - I just pulled the tubes and everything was perfect - no blown fuses
all voltages spot-on. Now I have to figure out what's up. Probably the brand new Russian Svetlana's I just put in it. That's all I can think of and most likely culprit.

[chabby-ao]

Thanks so much everyone - it works great now and seems to be operating perfectly! Damn Russion tubes-lol! I bought a whole bunch of Svetlanas because I got a good deal on them and liked them in a couple different Marshalls I've had. But one out of 3 I got were bad. And accounted for a major part of my problems. You know that hum I cited earlier in the thread? Thats was a bad EL34 in V6. The amps is fixed now and I can't thank you all enough!

[chabby-ao]

I see that you guys already solved this while I was drawing my picture, but I post it anyway.

Here's how I see the amp is wired. What do you guys think?

You have it right - to continue the next part of the fuse should have a red wire going to the OT/CT and Choke CT and good to go.

Thank you!

[VMS]

Just out of curiosity, was it New Sensor Svetlana or winged "C" Svetlana?

[chabby-ao]

It was new sensor Svetlanas. But before I completely hate on these tubes it seems I may have other issues, just not sure yet. I am going to put a known working quartet in in a minute.

But now I've got the old eggs scrambling in a hot skillet sound going on - oh well at least it's a new problem, I'll be back in  few.

[chabby-ao]

Phase inverter has issues but not sure what.
All the eggs frying sounds stop when I pull the PI tube.
Here we go again...at least I have it isolated to the PI.

[phsyconoodler]

Likely in the preamp somewhere.Pulling the PI tube effectively disconnects the preamp from the output so you don't hear the noise anymore.
  Since you have had bad luck with output tubes,I suggest you try some different preamp tubes first before doing anything else.Also clean and re-tension those sockets.