Gibson GA19-RVT Falcon hum problem

[Leonc]

Just tried out my new (old!) Gibson GA 19 RVT. It's got an excellent sound with very nice reverb and really great tremolo...but it's also got a lot of hum and perhaps not quite as much volume as one might expect.

Details
The hum is quite noticable when the amp is turned on, nothing plugged in and the volume all the way down. As you turn the volume up (still nothing plugged in), the hum increases a bit up to about 7 or so then seems to die back very slightly by the time you get to 10. Plugging in a guitar makes almost no difference.

I've swapped out the rectifier and power tubes for some known to be good and it made almost no difference, though I was able to get quite a bit more volume out of it with the new rectifier...still might expect a little more volume from a 2x6V6. Unfortunately, I don't have any really "trusted good" 6EU7s.

Questions
So, in your experience, what kinds of things might commonly cause hum like this?

I'll upload a schematic in a bit. Please feel free to make suggestions on parts to look into or consider replacing. Thanks!

[Leonc]

Schematic:

Schematic (http://www.patchWErkz.com/LeonsGear/GibsonGA19RVT/Schematic.jpg)

Manual:

Page 1 (http://www.PatchWerkz.com/LeonsGear/GibsonGA19RVT/ManualPg1.jpg)

Page 2 (http://www.patchWErkz.com/LeonsGear/GibsonGA19RVT/ManualPg2.jpg)

Page3 (http://www.patchWErkz.com/LeonsGear/GibsonGA19RVT/ManualPg3.jpg)

[Blue Strat]

If the amp has never had a cap job, it's about 20 years overdue. All electrolytic capacitors should be replaced before doing anything else. This will likely kill the hum, but should be done even if it doesn't.

[Leonc]

No Mike, looks like 100% original components...

[Blue Strat]

No Mike, looks like 100% original components...

Then you know what to do ;)

[erksin]

Can I ask - what did you have the reverb set to when you noticed the hum at idle? The Falcon is weird in that your signal hits the reverb FIRST - then the preamp section (kinda like having a Fender outboard unit type arrangement).

The filter and coupling caps definitely need changing - that's your loss of volume and hum issue in a nutshell I think.

Once it's running properly, you can expect more volume than a typical Princeton Reverb (around 15-16 watts).

Don't let your tech toss those tubes before he tests them - I'm still running ALL of the originals in mine!

[erksin]

Another thing Leon, if you don't mind...

I can't make out the text of the manual - could you tell me what it says in reference to the Monitor jack and what it is used for?

Thanks!

[Leonc]

Erksin - thanks for the tips. Yeah, as Mike pointed out, I figured it meant "cap job" and you both are confirming this.

BTW, I don't know if you noticed but the uploaded images are quite large. If I click on them with my mouse, they become big enough to read. (There's an interesting note about putting the reverb unit on a "solid, non-vibrating" surface. Do they want you to remove it from the amp when playing?

Ya, it's rather weird how the signal passes through the reverb first! The hum is there with the reverb off altogether. It stays the same with the reverb up to about 7. From 7 to 9 there's a wee bit more hum and between 9 and 10, it gets notably worse.

Well, I guess I'm off to buy a new set of caps for the power section. Any suggestions on where to look? Or just the usual...CE Dist, Angela's, Mouser...?

[Leonc]

Erksin - BTW - the monitor is an ext. speaker jack. check the schematic. This is really pretty ironic because a previous owner wired a (shielded) cable from the speaker to a female jack which he drilled a little hole for in the back baffle. I've subsequently removed this fine little piece of work, heheh. Anyway, there's no mention of the monitor jack in the manual.

[Blue Strat]

Well, I guess I'm off to buy a new set of caps for the power section. Any suggestions on where to look? Or just the usual...CE Dist, Angela's, Mouser...?

I haven't looked at the schematic or cap values, but I can't imagine one of those 3 sources not having what you need.

[erksin]

Erksin - thanks for the tips. Yeah, as Mike pointed out, I figured it meant "cap job" and you both are confirming this.

BTW, I don't know if you noticed but the uploaded images are quite large. If I click on them with my mouse, they become big enough to read. (There's an interesting note about putting the reverb unit on a "solid, non-vibrating" surface. Do they want you to remove it from the amp when playing?

Ya, it's rather weird how the signal passes through the reverb first! The hum is there with the reverb off altogether. It stays the same with the reverb up to about 7. From 7 to 9 there's a wee bit more hum and between 9 and 10, it gets notably worse.

Well, I guess I'm off to buy a new set of caps for the power section. Any suggestions on where to look? Or just the usual...CE Dist, Angela's, Mouser...?

I don't know why I didn't think to click on the image... :jo

I think the cautions regarding the reverb is just Gibson covering it's ass as usual.

BTW - that's the worst owner's manual EVAR! :puh

Killer amp though - enjoy it man!

[capnjuan]

Just tried out my new (old!) Gibson GA 19 RVT....but it's also got a lot of hum and perhaps not quite as much volume as one might expect.


Hi Leon: Agree with the others about caps but you may also find that, if you have the 7199 model, you still have some background hum at idle even with fresh caps.

There are two versions of this amp's circuit; a 7199 version and 6C4 version where these tubes support the reverb function. Can't say 'always' with Gibson but apparently the earlier tweed versions have the 7199, I understand some later tweeds have either the 7199 or 6C4, and most of the time, the 'Crest' version has the 6C4; otherwise the preamps have the same 6EU7s.

The 7199 is an inherently noisy tube; can be on average nearly 100 times as noisy as a 12AX7. I rehabbed a GA19 'Tweed' / 7199 model and tried Sovtek and JAN 7199s, no difference. Took the amp to a pro who checked my work, bypassed this, and shorted that - still some hum; not too loud, not too annoying but it's there.

My copy is slight 'dark' which I attribute to the 6EU7s. I also have a GA18 tweed; both amps w/ Weber speakers, same power supply, OT, and power tubes and the GA18 is dead quiet at idle. The difference, while possibly the 6EU7s IMO is the 7199.

Love the amp, hope yours came out good.

capnjuan

[Leonc]

I don't know if you guys noticed but this thread was from back in May :)

Problems got resolved back then: replaced all electrolytic caps. No more hum. Tremendously quiet amp, actually.

[Trego]

congrats...when I first started playing guitar my uncle gave me a '64 Gibson Falcon. I turned it on and it hummed really loud. My dad decided that we should trade it in...not fix it. We got 50 bucks for it at the local music store (...jerks) and I got a Peavey Audition 110...

worst trade+cash of my life

anyone want to sell me a Gibson Falcon?

[AlexK]

congrats...when I first started playing guitar my uncle gave me a '64 Gibson Falcon. I turned it on and it hummed really loud. My dad decided that we should trade it in...not fix it. We got 50 bucks for it at the local music store (...jerks) and I got a Peavey Audition 110...

worst trade+cash of my life

anyone want to sell me a Gibson Falcon?

Ouch, that really sucks. A Crestline Falcon was given to me by a great uncle who needed me to sell some stuff for him on eBay and I'm in love with this amp. When he gave it to me there were a lot of problems (blown speaker, needed a cap job BAD, and springs in the reverb tank were broken), but now it is just a killer amp.

[JJman]

Since we are playing "the Gibson my uncle gave me"

My Uncle gave me his '63 Epiphone Wilshire a while back. (Yes Gibson made it.) I see pristine examples advertised for 2-3 grand sometimes.

My nephew will probably be surprised some day when he gets my stuff.

Here's to Uncles :BEER