Alamo Challenger amp -Help, new guy!

[glenn.b]

I recently ended up with a 1967 Challenger by Alamo-Here is what I have done since:
1. Re-tubed. 5y3 was an original, the other ones where Sovtecs, which I am not too fond of. Turning the amp volume above 7=bad harmonic sounds. My estimate was the tubes were shot.
2. 3 prong power cord -tired of getting shocked.
3. New speaker installed
4. New caps added-.047 /.022 values...glad I did, as I went to remove the old frail .047 poly cap on the pre amp, it just fell away at the touch of my pliers!

Here's the catch. The amp turns on fine, runs fine-to a point. Taking the volume knob past 5 , it sounds like a tremolo, a soft "whump whump" sound, steady. Looking at the tubes, I see the 6v6 has a bit of a blue light flashing in accordance with the tremolo sound.
I have mostly been pedal building, but I am capable of making the chassis safe to work on; but what I am completely lacking in is experience. If anyone could offer suggestions, I'd be very appreciative. Thanks!

[Structo]

Sounds like motor boating.

Did you replace the power supply filter caps?

This could be from the filter caps or leaking coupling caps.

Also tubes should always be the first suspects when getting an old amp going.

[glenn.b]

This little amp never had the big huge filter caps...just two poly caps, one on the 5y3 (.022 ) and the other poly, the one that fell apart off the 12ax7 ( .047) the other 3 replaced were the ceramic types .022 as well. I did not replace with ceramic ones, but I had on hand Mallory .022 . Thank you a ton for the responding...

[Structo]

Does it look like this?

[glenn.b]

That is it, but I did not use ( mistake on my part likely) when re-doing-simply used visual references such as the old caps to re-cap...geez, I hope I did not goof! I've seen on the web where some folks have questioned the accuracy of this one. Again, thank you ! I'm new with this, so very capable of messing up...

[selloutrr]

can you try the tubes in another amp or tube tester to confirm they are not the problem?

next test caps.

you might want to go back and touch up all your solder points just to make sure you have no cold solders.

If you have any doubt in the schematic use it as a reference, make a copy and draw in anything that is different between your current wiring and the schematic.
post it and we can help walk you threw.

[glenn.b]

Can do! That second one might take a bit ( forgive me , I am a bit slow with the schematics, still) but the add solder / joint re-flow / triple check I'll will get right on, again, thank you.

[jjman]

The filter caps are the ones with a value of "20." They may be one of those "cans" that has a few terminals on it.

Got a pic of the chassis?

[glenn.b]

Sorry, I failed to answer the first thing you pointed out. I have no test equip for tubes, nor another amp that accepts this group of tubes. I got those tubes new just a week and a half ago, and they ( and the amp) did not do this sound 'till last night, when I changed the power cord out for a safer one and that caps...By the way, the tubes are(by brand) 12ax7/6v6 -both JJ's. the 5y3 is a 5y3GTW,NOS RCA

[M Fowler]

Do you have a digital camera so you could take some pictures and post for people to help you?

Mark

[glenn.b]

Darn! No I dont have any pics that are good enough for this....The household digital camera is out with my daughter...

[IMG667]http://i895.photobucket.com/albums/ac15 ... CT0507.jpg[/img]



Sorry all, this is what I have for now. I appreciate it, 'tho...

[glenn.b]

these were the cap changes made:

[IMG667]http://i895.photobucket.com/albums/ac15 ... hanges.jpg[/img]

[glenn.b]

Hey JJman, there is a HUGE metallic cap, says Mallory on it, as well as 20/450... filter cap?? ok, very new with amps, if this is a cap it just does not look like anything i'd think of as a cap. It is soldered on the underside to a few really large resistors

[selloutrr]

BEcareful removing that CAN CAP it holds voltage!!! you need to drain the cap before it's safe to remove.

you can get a replacement at www.tubesandmore.com

search capacitors
electrolytics
cans

and match the values it's OK it increase the voltage but not lower it. the MFD/UF needs to be as close as possible
i.e. 40mfd @ 450Vdc
47mfd @500V is ok 33mfd @ 350V NOT OK!!!!

[dano-rator]

I'm jackin an old thread here:
So, the first stage is grid leak biased? What's up with the seemingly low-ish grid res? Most of what I see is in the megaohms, here it is 220k? I am wholly unfamiliar with grid leak bias. Any insight is appreciated.

I just picked one of these up for cheap. Sounds really good I think... added a fuse (cause I like my stuff off fire) and a grounded chord, re-soldered the grounds on the can cap and its a lil ripper!

Dan