Yes, 100nF and 47nF.  They should also have a voltage marked on them.  Do not use them in a circuit that will exceed the voltage rating.

The value is in between the letters, so 473 and 104 for those.
The first 2 digits are significant, the 3rd digit is the multiplyer, giving the value in pico-farads.  So for the multiplyer, add that many zeros to the significant digits.
So in this case, 47000, and 100000 pico-farads.
To convert to nanofarads, move decimal place 3 digits to the left.  You get 47 and 100 nano.
To convert to microfarads, you move decimal place 6 digits to the left (from pico).
So .047 and .1 microfarads.

Quote from: Roly on May 20, 2014, 02:30:39 PM
Quite likely not;

Title: GFX120a
No: 07S252-XX
Sheet: 1 of 2
Date: 6/19/98

The basic point is that one has extra bypassing the other doesn't, and this change in DSP supply arrangement may be a clue they were having some problems in this area.

Yes, that is the same drawing I have.  It's a 470 ohm (R88), not 47.
It is used as a voltage dropper because they are tapping off the +40V supply.  The other circuit has it's own winding and rectifier for a separate supply and has a 10R resistor.
I'm not arguing that the .1uf bypass cap may help, I just wanted to point out that the supply circuits are quite different and the 470R is not just for filtering.

Agree to try the .1 bypass as close to the DSP chip as you can and see if it helps!

 Roly, the schem. with the 10 ohm has its own supply, not running off the 40V line.
The gfx212 schem. shows a different supply and 470, not 47 ohm.  Are we looking at the same schematics?

Quote from: smackoj on May 13, 2014, 07:31:29 PM
Ola amigos; I have a Lab Series L7 which I am pretty sure is the same amp with 4 ten inch spkrs instead of 2 twelves. I can only get normal volume using one low gain input.

First, the inputs are labelled different than what we normally see, HI means for high output pickup, so there is less gain with the HI inputs.  The LO inputs will give more gain.
Each pair of inputs goes to same IC.  So for your channel that has 1 input working, the other input must have a problem with the jack or solder.  If a channel input IC is bad, neither jack for that channel will work.
  So you may have a few separate problems here.

Quote from: Brhibler1 on May 13, 2014, 05:11:08 PM

Quote from: g1 on May 13, 2014, 03:56:55 PM
  Put a patch cord between preamp out and power amp in (dry), any difference?

That had already been checked. I'm an experience amp tech, 

lol, that post was supposed to have gone here: http://www.ssguitar.com/index.php?topic=3472.msg25990#msg25990
Sorry about that, you must have been scratching your head wondering why I would think the loop could cause that and what the "dry" was about. 
I would have thought the lf351 ok as a lf356 sub, but, as you say, maybe it was defective. 
  Or maybe someone else here more familiar with the circuit will comment on whether there is a problem using the lf351 in this spot of the circuit.

  Put a patch cord between preamp out and power amp in (dry), any difference?

Edit:  This post was supposed to go in here: http://www.ssguitar.com/index.php?topic=3472.msg25990#msg25990
Sorry for any confusion.

  Couldn't find any free schematics, but available for sale here:
http://www.hansenguitars.com/engine/inspect.asp?Item=422&Filter=Amps

Quote from: Roly on May 02, 2014, 02:20:16 AM
Another odd fault that old Fenders can exhibit when the electros are going down is that the volume goes down to zero at about 1 or 2 on the knob, then comes back up again from there to zero.

Roly, which electrolytics cause this, cathode bypass caps or supply filters?

  Excellent point Dr.Gonz.  I don't know if the ads here are enough to cover Joe's costs to keep the place running.  If he wanted to put on a "donate" button or run a fundraising drive, I'd be more than happy to donate, this site is greatly appreciated!

  Blending is not possible.
Switching is only easy if you turn off both amps.  Otherwise you need a fairly sophisticated switching box that makes absolutely sure the first amp is disconnected before the second is connected.
  Both amps connected to the same load at the same time usually ends in smoke, flames, and tears.

  Well, the only good news is I tried to buy the domain name through the godaddy link and it said the "domain is not available".
Dr.Gonz, thanks for the reminder about the paypal thing.  In case it's a financial issue I sent a donation via paypal to paypal (at symbol) firebottle.com.  Those donations are accompanied by an email to him titled "you've got money" so I think he will have it set up so those don't go into his spam folder  .  Added a note about hoping to see the site back up, so if he was unaware of the issue he should be notified now.

  Yes, I think that is the issue; the schematic shows 100V but he only has 80V.  Like Enzo said, don't worry about it.  In the world of tube guitar amps, that is actually close enough.  The current through that 270K is what sets the voltage there.  It will change a little bit for every individual 12AX7 you try.  If you have some other 12AX7's try them, you may find one that gets you closer to 100V.
You have 232V on one side of the 270K, and 80V on the other.  That is a difference of 152V.  Ohms law says I=V/R, so 152 / 270,000 = .00056, or .56mA  So we know the current through your tube is about 1/2 a milliamp.  But let's solve for their tube in the schematic, 232V on one side of resistor, 100V on the other side.  Difference of 132V.  132 / 270,000 = .00048 or .48mA  Very little difference, both their tube and your tube are running about 1/2 a milliamp and well within the variation we normally see with tubes (+/- 20%).
  And, like Enzo said, that DC voltage does not go to the 6V6, C6 blocks DC but lets AC (signal) through.  If there was DC getting through C6 to the 6V6, it would mean C6 was defective and (leaky).

Quote from: smackoj on April 28, 2014, 09:26:17 PM

Yes, you need polarized electrolyic caps to replace the main filter caps and the bias cap. Be careful to ensure you replace them with correct polarity observed.

And a reminder:  The bias cap has it's positive end going to ground.  This is opposite of all the other electrolytics and is normal and correct.

  They didn't change much till the boost version so I'll attach the standard schematic and layout which should be close.
  The bias filter cap is the white mallory on the little board by the pilot light.  Replace it with something bigger with a higher voltage rating, like 100uf@100V.  All other caps should be replaced with same value, but can be higher voltage rating.
  After you have replaced the main filters, and the bias filters, there are only a few more electrolytics, so you might as well replace them too.
  The blue ones are non-electrolytic.  They are being used as coupling caps.  They block DC voltage from getting where it is not wanted, but they let the AC signal pass through.  They last much longer than electrolytics and generally don't go leaky for any particular reason.  Some brands/types are more failure prone than others, the blue ones used in the old Fender amps are usually not problematic.