The Defpom Forum, for RadioMods, S&M Software and Music by The Defpom

Ok here is a good puzzle for the more experienced Techs.....

I have a Firebird F-500. It has 4 tubes (1 driving 3). It has 3 switches and two knobs on the front... the first switch is Standby and Transmit... the second is Power on and off.... the 3rd switch is AM and SSB.

The two knobs aren't marked but I'm assuming the first is Load and the 2nd is Tune....

Everything lights up and looks good.... all tubes come on and everything appears functional..... then when you turn it from standby to TX and key the radio the points kick in but the amp doesn't function?? In fact I used a radio that was keying 4 watts and swinging to around 12 watts to test it and with amp in standby meter shows 4watts key 12 watts swing.... with amp in TX points kick when radio is keyed but the meter shows nothing!! I have keyed the radio and moved both knobs and still couldn't get anything from the amp!!!

Could someone please help?????



UPDATE-----
I was going back through this thing again using the schematics as a reference and I discovered a capacitor change from the schematics.....
On the right hand knob facing the front of the amp... I think this is the Load?? on the back side it has a coil connected to the center collector of the tubes by a capacitor which in the schematics shows to be a .01 uf disc cap, however the actual cap being used is two .0033 uf caps in parallel. Upon closer inspection I found both of these are burnt at the leads and one of them has been "blown" loose at one end... I'm going to say this is probably the problem with the output of this unit! Here is where I have the question...
I don't have a ceramic cap of that size available could someone tell me what I could use as a substitute? And is it possible to replace that cap with an electrolytic cap of similar value?

Here are the numbers on the old cap..... unsure of what schematics call for it just say .01 uf?

AU
RMO
.0033 M
Z5U

Any and all help would be excellant!! Thanks in advance!!!

Don't fit an electrolytic cap, replace like for like.

Replace the other ceramic disc capacitor(s) with a ceramic disc capacitor of .01 uf and a voltage of 1-2kv. These are pretty common, you can get them reasonable. Make sure the new one has an operating voltage of 1kv or better (2kv is best) or otherwise, you'll pop the new one.


Regards,
Rick (Triple 7)