Silkyn Super 50 blowing power tubes V7

jtcnj said:
I kind of stalled - thanks for the specifics and staying with me on this.
I will swap those PI coupling caps out this weekend if I have them on hand - I think I do.

The resistance between each pin 3 and the center tap (B+) has always been 19.4-19.5Ω for both, with the tubes in, power off.
I will check it with tubes out; it should be the same I would think.
Click to expand...
The PI coupling caps are not what most people would suspect.
But those little buggers can sneak up on you.

The purpose is to block PI high voltage from leaking into the output bias voltage.
But just a little leakage can cause a big headache...
And sometimes that leakage is intermittent not constant....sometimes leaks, then it stops, then it starts again.
It can drive you nutty. Of course this doesn't happen in all amps and it's hard to catch it when it happens.

Tubes out.
Standby on operate position.
Set meter for DC volts...
Now put red meter probe on one lead of the PI coupling cap.
Black probe on the other lead of the same PI coupling cap.
Now read the entire DC voltage, ACROSS the PI coupling cap.

It's a higher voltage than the highest B+ voltage anywhere in the amplifier....
and typically much higher than the cap is rated. No wonder it leaks.

Now you start to see why I use 630V caps for the PI coupling.
The blasted things are almost always underrated, from the factory.
 
WavMixer said:
I still have 2 of these Silkyn Super 50 amps packed up in storage.
Click to expand...
Grant, I did the reverb and "mandatory" dirt channel mods, along with the new PT (though mine never fried) and I'm really digging this amp.
And, I get reminded just how good the clean Blackface type channel is every time I plug in.

I do my warm ups and some chord fingering exercises, and play a little surf. Plus, the RAT especially sounds really good through the clean channel.
The reverb is almost ferocious now, not as pure / lush / good as the Fender standalone 6G15, but yeah, it is really good.

And the speaker seems to have just gotten better over time.

Just cant really crank it that often.
 
I also did the mods on one of the amps, the other is stock. I also purchased a PT, but have not installed it yet. My world got rocked 3 years ago and most of my possessions have been in storage until we buy a new home.
 
My $150.00 Mesa MK3 100 watt blue stripe combo failed PI coupling cap 200 volts on one side of the bias some day will re cap the amp
what a pain to pull the main board I did get a great EVM12L speaker out of the deal that now lives in the ODS Green Hornet amp.

Mesa MK3 002.JPG

Green Hornet 3 001.JPG
 
67plexi said:
My $150.00 Mesa MK3 100 watt blue stripe combo failed PI coupling cap 200 volts on one side of the bias some day will re cap the amp
what a pain to pull the main board I did get a great EVM12L speaker out of the deal that now lives in the ODS Green Hornet amp.

View attachment 87466

View attachment 87467
Click to expand...
It's possible to change the PI coupling caps without pulling the board.
I have done it that way because I hate :eek: pulling the board out.

Taking the board out is absurd but sooner or later you have to do it.
I socket all the relays and ICs as long as the board is out.

In a Mesa, one relay socket can save five hours of labor...
 
Amp Mad Scientist said:
It's possible to change the PI coupling caps without pulling the board.
I have done it that way because I hate :eek: pulling the board out.

Taking the board out is absurd but sooner or later you have to do it.
I socket all the relays and ICs as long as the board is out.

In a Mesa, one relay socket can save five hours of labor...
Click to expand...

5 hours????
 
Thing is the amps 34 years old I will change out all the capacitors have them in stock and test all other components
I know AMS is being easy on the five hours I got my Mesa experience from one of the cruse ship lines repairing over 1300 Mesa amps
the worst part was net 120 days payment on parts and labor next was 1100 Fender amps I turned them down.
you could say I got burned out on Mesa products I'm back to my tool making company.
 
Inspector #20 said:
5 hours????
Click to expand...
If you have ever taken the board out of a Boogie....
5 hours is quick. :pound-hand:
The maintenance is rather absurd.

If a relay goes bad, or an IC chip, or anything else that is soldered in as such.....
You have to pull the entire board to change it.
Which makes the maintenance cost and downtime astronomical....

Which is why I install mil grade sockets for everything, whenever the board is pulled.

1670684827680.jpeg I get some Mil-Max sockets, and socket everything.

The next time a relay goes bad: Plug in a new relay - easy.
It takes 15 minutes to change it, not 5 hours.
This will save the amp owner hundreds of dollars and weeks of downtime, over the next many years.
 
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Amp Mad Scientist said:
If you have ever taken the board out of a Boogie....
5 hours is quick. :pound-hand:
The maintenance is rather absurd.

If a relay goes bad, or an IC chip, or anything else that is soldered in as such.....
You have to pull the entire board to change it.
Which makes the maintenance cost and downtime astronomical....

Which is why I install mil grade sockets for everything, whenever the board is pulled.

View attachment 87538 I get some Mil-Max sockets, and socket everything.

The next time a relay goes bad: Plug in a new relay - easy.
It takes 15 minutes to change it, not 5 hours.
This will save the amp owner hundreds of dollars and weeks of downtime, over the next many years.
Click to expand...

Wow!!!

I did not know that!!!
 
Amp Mad Scientist said:
Have you done the high voltage tests?

Standby turned to operate, tubes out.
DC Voltage on pin 3 of each output tube socket?
DC Voltage on pin 4 of each output tube socket?

Power disconnected, tubes out.
Resistance between pin 3 to pin three of both sockets?
(the resistance of the output transformer primary, pin 3 to pin 3?)

The resistance between pin 3 of one output tube socket, and the output transformer primary center tap?
Now, the other pin3 and center tap?
Click to expand...
Power up, standby off
No power tubes, voltage to ground for pins 3 and 4, both sockets: 516v.

Power off (caps discharged)
Resistance across each side of OT (Pin 3 to CT / B+):
V7 - 19.1 Ω, V8 19.2Ω (mostly this has been 19.3 - 19.4Ω the many times I have checked it while biasing).

Pin 3 to Pin 3: 37.7Ω. (I would expect ~38.3Ω , dunno)

20221211_130447-2.jpg




I replaced the coupling caps from the PI to the power tubes, after mapping the components and marking up the schematic.
The one to V8 - the yellow (C25), is different from the one to V7 (C24). Both are J223 400v.

Replaced with Mallory 0.022µf 630v. I polarity tested them at the input of another amp, but could not hear a difference.
Dont know why the pic is rotated.
With tubes back in, the voltage across them is @383v at idle (as I recall, didn't write it down) - pretty close the 400v rating, as was mentioned.

20221211_154829-2.jpg

After letting it warm and monitoring @30min:
At a bias voltage of -52.8v at pin 4 both V7 and V8, the voltage drop across the OT halves is: V8 .695v, V7 .715v.
.715v/19.1Ω = 37.4ma x (B+ 494v) = 18.5w/30w = 61.6%.

I have not played it yet, do things appear to be in order?

When I eventually do, I will with the chassis out of the cab and watch for red-plating.
 
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