Fender Hot Rod deluxe

[tim]

[QUOTE=Enzo;8786]Pardon me? The rail in the drawing above is 42 volts. The 470/330 ohm resistors feed 16v zeners. They are current limiting resistors, not dropping resistors strictly speaking. That means ther will be 26 voltas across each resistor no matter what value you use. And that mean the 330 ohm will run even hotter than the 470. I do not recommend that change.QUOTE]

You're right Enzo.....egg on my face and all that.... I had just got done reading the write up on the "Unofficial HRDx pge" and without consulting a schematic, I was under the assumption that they were simply doping resistors....the sad thing is that I have fixed literally hundreds (maybe into the thousands) of these series amps and forgot that these were I limit resistors used in the zener regulator circuit.
Anyway, one thing I use to help the solder stand the heat is use silver solder....it seems to help.

[JC@]

Yes I like to use a solder material that has a small amount of copper in it.
I can't remember it's brand name, but I believe it is made in France. The label on the spool is dark red metallized paper, but I only find it in a shop that is in another town so I usually end up using the Sn60Pb40 type one.

Well, back to the HRD:
That nasty noise is now gone I believe.
C36, the 22/500 electrolythic cap that filters the B+ for the preamp tubes needed some resoldering I must admit That was very hard to find, because it was just a cold solder point aggravated by the solder starving technique used in this amp.

Anyway, I have learned a lot about these amps and that for sure that will help me in the future.

[Rick Erickson]

Also change the 470's to 330's.....30% less voltage drop across each one which means they run cooler and the solder joints under them last longer.

At the expense of the solder joints under the 5W Zeners which will run that much hotter. I prefer to install Vector T-42 & T-28 Flea-Clips (or similar stand-off) under the resistors and 5W Zener diodes to lift them away from the PC board. Solder them in place with silver bearing or other hi-temp solder. This keeps the heat off the circuit board, as the flea-clips act as heat sinks and the hi-temp solder doesn't break down as easily under normal operating temperature. If done properly, you should not have to deal with a loose connection there again.

RE

[Rick Erickson]

The rail in the drawing above is 42 volts. The 470/330 ohm resistors feed 16v zeners. They are current limiting resistors, not dropping resistors strictly speaking. That means ther will be 26 voltas across each resistor no matter what value you use. And that mean the 330 ohm will run even hotter than the 470. I do not recommend that change.

Enzo - You are correct - I tried to respond to this but didn't think it through as far as you did - the 330's will indeed run hotter as will the Zener Diodes due to increased current through them.

RE

[Enzo]

Now and then I DO get something right. Please inform my wife.

[KarbonHed]

A site dedicated to the Hot Rod

http://studentweb.eku.edu/justin_holton/

The one I have seen and fixed had the same kind of symptoms you have and it seemed closest to "the plate load problem" discussed on this page http://studentweb.eku.edu/justin_holton/plateloads.html

Very easy fix if that's what the problem turns out to be.

[JC@]

Yes I also changed all plate resistors while I was there, but the real problem was C36, a 22/500 electrolythic cap that had a cold solder joint.

[tim]

Now and then I DO get something right. Please inform my wife.

You can give this to her......

ENZO WAS RIGHT THIS TIME!!!!


Glad I could help....