Fender Champ problems

[kevinlekiller]

Hi guys, been reading this site for a few months , love it!

Well I got a champ a few months ago ( those reissue ones ). It didn't sound right so I looked online and found John Frondelli's mods. One thing I always noticed was the amp is VERY hot ( you can barely touch the chassis metal after an hour ). Another thing is people online said it breaks up at mid volume ( past 9 or so), mine didn't break up even at 12(max volume).

A problem It had was it would do a ticking noice ( tick tick tick etc..) I figured it was the output tube, so I bought one with a 12ax7 when buying the parts from antique electronic supply.

So I did the mods and the amp sounded pretty good but it didn't break up at max volume still . The new tube was extremely hot like the original one, and the amp started making the ticking noise after a days.

Then I read online on speciatlyguitar.com that the champ should get a higher cathode bias resistor , so I put in a 600ohm 4watt vs the 468ohm 2watt stock. But the tube still ran extremely hot and the ticking was still present.

I decided to check the voltages from the test points on the schematic but I'm not an expert and the DC voltages look ok , but I don't know how to get the AC voltages from some points (tp9 tp2 tp5 tp13).

Here's the list of the test points (checked them a few times because my wall voltage varies alot):
tp16 114 to 126 vac = wall voltage
tp15 5.7 to 6.3 vac = heater voltage from transformer
tp14 278 to 294 vac = voltage from transformer
tp12 365 to 369 vdc = b+ voltage ( after the rectifier)
tp11 362 to 365 vdc = (b2?)
tp10 342 to 344 vdc = (b3?)
tp8 21 to 24 vdc = cathode on 6v6
tp7 & tp6 = 1.7vdc cathodes on 12ax7

My questions are , why do the tubes run so hot ( even the preamp tube runs pretty hot ). Do those voltages ( the ones I got right ) look good ? What is causing the ticking , are the tubes prematurely failing? Heat? Should I check any other points on the board.

Thanks and sorry for the long post!

Edit: Forgot to post the schematic!

[Mandopicker]

As far as the heat goes, these amps do get hot - as do all tube amps. Not unusual for Single Ended Class A amps either. Does your amp seem to getting too hot relative to others...that is hard to say, but the voltages look reasonable.

Questions:
How hot is the power transformer relative to the overall amp temp? Can you touch the trans when the amp has been running for a while. Basically, what seems to be causing the heat...the tubes or the transformers or both. Each symptom is caused by different things.

As far as the ticking: Does the ticking occur no matter where you plug the amp in? Or otherwise said...do you always plug the amp into the same outlet when playing?

While your modding it...you should also upgrade all the resisistors to at least 1/2 watt, phase inverter 100K's should be 1 watt, and the 2 x 100ohm's for the artificial center tap of the filaments should be at least 1/2 watt, but 1 watt wouldn't hurt. I have modded a few of these and also found that bigger and better filter caps helped a great deal as well. Just be careful, as the PCB board traces are delicate. Remove the board and use a solder sucker for the best results.

All This will make the amp more quiet and reliable. (I would also only suggest doing this major overhaul once you have the Ticking figured out.) Always best to mod a perfectly running amp.

Good luck and have fun.

[kevinlekiller]

Hi Mandopicker, thanks for the reply.

I forgot to precise these points in my original post. The heat definitely seems to come from the output tube, the power transformer gets a little hot because the output tube is like 2 centimeters beside but it takes a while before its very hot ( like the chassis ). The preamp tube doesn't get hot like the output tube. The output tube after 1 minute is untouchable ,it would be dangerous to touch it.

Same for the ticking ,forgot to go into detail. I can turn on the amp put it on 12 with nothing plugged in and its very very quiet. If I plug in my guitar then there is some hum from the pickups ( turning down the guitar volume makes the amp silent again ). If I start playing the guitar ( I tested this with all my guitars ) the ticking begins. I tried different cables , plugging into a different outlet. I don't have this ticking with the same guitars and cables on my other amps. As soon as I stop playing the ticking stops. Its not linear, sometimes it will do it a few times in a row , sometimes it does it once and I don't hear it for another 20 seconds.

As for the resistors, I replaced a few of them for higher wattage, will buy 100k 1 watt's when I buy the new tubes. For the caps, should I replace the 4 of them? 47uf ?

Thanks!