Weird tremolo problem with a GA-5T Skylark

Gibson, Valco, Gretsch, and more

Re: Weird tremolo problem with a GA-5T Skylark

Postby bloodspoint on Fri Jun 30, 2017 8:15 pm

stratele52 wrote:Since May 16, did you replace the 3 tremolo caps ?



No. I have not even had time to identify the three tremolo caps, let alone replace them. All I have had time to do is try swapping the two tubes around. Unfortunately, working on amps is about 17th on my to-do list, and I rarely get past about 3rd or 4th on the list.
Bloodspoint Studio
"This is our concern, Dude..."
bloodspoint
Court Jester
 
Posts: 87
Joined: Wed Oct 17, 2001 7:01 am
Location: Morrow, OH USA

Re: Weird tremolo problem with a GA-5T Skylark

Postby stratele52 on Fri Jun 30, 2017 8:24 pm

Most of the time, if it is not the tube, it is one or more cap. I don't waste my time, I replace all 3, so cheap to buy.

Good luck.
stratele52
Knight
 
Posts: 1904
Joined: Sat Aug 21, 2010 9:35 am
Location: Québec province, Canada

Re: Weird tremolo problem with a GA-5T Skylark

Postby bloodspoint on Fri Jun 30, 2017 8:27 pm

stratele52 wrote:Most of the time, if it is not the tube, it is one or more cap. I don't waste my time, I replace all 3, so cheap to buy.

Good luck.



Good point. If I get in there, especially as "entwined" as everything is, I'll replace all of them at once.
Bloodspoint Studio
"This is our concern, Dude..."
bloodspoint
Court Jester
 
Posts: 87
Joined: Wed Oct 17, 2001 7:01 am
Location: Morrow, OH USA

Re: Weird tremolo problem with a GA-5T Skylark

Postby zarfnober on Sun Jul 02, 2017 12:39 pm

, I'd have to come up with new tubes. I don't have any extra 6AQ5 or 6EU7 in my parts stash.

I have some NOS Mullard 6AQ5 tubes, pm if interested.

Rocco
zarfnober
Peasant
 
Posts: 47
Joined: Wed Mar 19, 2014 2:23 am

Re: Weird tremolo problem with a GA-5T Skylark

Postby stratele52 on Sun Jul 02, 2017 7:45 pm

Tremolo issue , look it is not the tube anyway.
stratele52
Knight
 
Posts: 1904
Joined: Sat Aug 21, 2010 9:35 am
Location: Québec province, Canada

Re: Weird tremolo problem with a GA-5T Skylark

Postby bloodspoint on Thu Jul 13, 2017 11:03 pm

All right, so I see four caps in there that are .01 or .02, connected in some way to V2, which is the tremolo tube. The last .01 goes to a ground strip. They're all ceramic discs. It looks like it would be easy enough to replace all four of them, though I'll probably have to source some, since I may not have any of the .02's around.
I have several ceramic discs about 3/4" in diameter that say .01 1000V, are those okay for the .01's? They're larger than the ones in there, which are all around 1/2" in diameter.
My multimeter has a capacitance function, but it only has an "nF" range, and the .01 1000V caps I mentioned above all read something like 19.57 nF on that.
Is ceramic disc okay for this application, for all four of them, or should I be looking for something else?

Thanks,

Sean
Last edited by bloodspoint on Thu Jul 13, 2017 11:43 pm, edited 3 times in total.
Bloodspoint Studio
"This is our concern, Dude..."
bloodspoint
Court Jester
 
Posts: 87
Joined: Wed Oct 17, 2001 7:01 am
Location: Morrow, OH USA

Re: Weird tremolo problem with a GA-5T Skylark

Postby bloodspoint on Thu Jul 13, 2017 11:07 pm

Also, am I reading correctly above, that there is ~110VDC at that part of the circuit, so I will need to shoot for say, 500VDC rated caps?

I have a ton of ".022" and "223" green chicklet caps I've used in guitars, but not sure if the value is correct.
Last edited by bloodspoint on Thu Jul 13, 2017 11:28 pm, edited 1 time in total.
Bloodspoint Studio
"This is our concern, Dude..."
bloodspoint
Court Jester
 
Posts: 87
Joined: Wed Oct 17, 2001 7:01 am
Location: Morrow, OH USA

Re: Weird tremolo problem with a GA-5T Skylark

Postby bloodspoint on Thu Jul 13, 2017 11:27 pm

If someone can point me at a part number for Mouser or Digikey or somewhere I can find the right ones, I'll get them there.

Okay, so here, searching for ".01 ceramic disc capacitor 1000V", I get this:

http://www.mouser.com/ProductDetail/Vis ... cuPQNRo%3d

Where it gives the capacitance as .01 uF (that's supposed to me a "mu", 10nf, and 10,000pf, which helps explain some of the different values I see for the same parts.
Bloodspoint Studio
"This is our concern, Dude..."
bloodspoint
Court Jester
 
Posts: 87
Joined: Wed Oct 17, 2001 7:01 am
Location: Morrow, OH USA

Re: Weird tremolo problem with a GA-5T Skylark

Postby bloodspoint on Thu Jul 13, 2017 11:40 pm

Here is what I'm looking at, BTW. At the top left, just out of the pic, is the back of the "Loudness" pot:

Image
Last edited by bloodspoint on Sun Jul 16, 2017 2:48 am, edited 1 time in total.
Bloodspoint Studio
"This is our concern, Dude..."
bloodspoint
Court Jester
 
Posts: 87
Joined: Wed Oct 17, 2001 7:01 am
Location: Morrow, OH USA

Re: Weird tremolo problem with a GA-5T Skylark

Postby stratele52 on Fri Jul 14, 2017 8:10 am

These are al Micro farads.
Order them from ;
http://hoffmanamps.com/MyStore/catalog/Capacitors.htm

Scroll down to middle of the screen.

IMO any kind of cap with same value may work, like Orange drop
stratele52
Knight
 
Posts: 1904
Joined: Sat Aug 21, 2010 9:35 am
Location: Québec province, Canada

Re: Weird tremolo problem with a GA-5T Skylark

Postby bloodspoint on Fri Jul 14, 2017 12:56 pm

Thanks! Ordered some replacement caps, so I'll let you know the result once I've replaced those. Does it make sense to replace all four in the pic above, or are only the three in from related to the tremolo?

Sean
Bloodspoint Studio
"This is our concern, Dude..."
bloodspoint
Court Jester
 
Posts: 87
Joined: Wed Oct 17, 2001 7:01 am
Location: Morrow, OH USA

Re: Weird tremolo problem with a GA-5T Skylark

Postby bloodspoint on Sat Jul 15, 2017 7:56 pm

UPDATE: Okay, so I tried replacing all four of those .01 and .02 caps. Zero difference. None. I experimented around some while I was in there, as well, and found that adding capacitance, e.g. from .01 to .02, basically slowed the rate by ~half, and bypassing any individual cap essentially deactivated the tremolo effect.
Switching V1 and V2 has not effect. Taking V2 out altogether, the amp still operates, but considerably less gain, and of course, no tremolo effect.
I also tried bypassing or using different values across that 4.7M resistor. If I bypass it, the tremolo goes away.

Again, the splat noise is only when the tremolo is on, and only on the attack, though if I hit really hard, there might be lesser, decaying amounts of splat as the beats progress a few times.

If I pluck very softly, I don't get as much, and I get less of it with lower output pickups.

So my theory now is there's too much gain going into that tremolo circuit. Anything I can do to attenuate that? I had the idea to bypass the 4.7M with a pot, and see if there was some setting that seemed to stop the spitting noise, but not stop the tremolo. Of course, the problem is, I don't have any pots near that big. Biggest I use for anything is 1M, and that, even all the way down, only gives me... 1M of resistance.

Open to any ideas before I just put this thing back together and sell it as a cool, clean old little amp, and hope the potential buyer doesn't care about the tremolo effect. Aside from that, it's a great sounding amp.
Bloodspoint Studio
"This is our concern, Dude..."
bloodspoint
Court Jester
 
Posts: 87
Joined: Wed Oct 17, 2001 7:01 am
Location: Morrow, OH USA

Re: Weird tremolo problem with a GA-5T Skylark

Postby pdf64 on Mon Jul 17, 2017 1:01 pm

Do the power tubes definitely have those 22k control grid stoppers as per the schematic, mounted with the resistor body close to the socket terminal #1/7?
If not, fit them.
If so, suggest you try 100ohm 1/2 watt grid stoppers on each screen grid socket terminal #6, and a 10k grid stopper to the 2nd stage 6EU7, the one fed from the volume control wiper.
If that doesn't help, it may be that the trem modulation is just too deep, and its amplitude needs reducing, in order to maintain stable operation.
Suggest that a 100k resistor is added in series with the 0.047uF coupling cap at the output of the oscillator, and that the 330k resistor to chassis 0V (at the node of the power tube grid leaks) is reduced to 220k.
My band:-http://www.youtube.com/user/RedwingBand
pdf64
Knight
 
Posts: 1243
Joined: Thu Dec 14, 2006 9:55 am
Location: Staffordshire UK

Previous

Return to Miscellaneous American Amplifiers

Who is online

Users browsing this forum: No registered users and 2 guests