Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Tristan on February 15, 2011, 01:27:21 pm
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Hi all *new member, first post :angel *
For a while now I have an ELK guitar man amp. It's a really nice clean amp from early '70 with reverb and 'vibrato' (tremolo). It works fine but when I activate the tremolo it is barely noticeable. So my question is, is there any way to make the tremolo more intense? It has a speed and intensity pot but even when they're fully open there isn't much of a tremolo IMHO.
Here are some schematics of what is most likely my amp, because I can't find the schemes for exactly my amp model, but these should be alike because it should have the same amp chassis and tube config: http://www.drtube.com/schematics/elk/twinamp50.gif
My amp has 2 speakers, 2 channels (rev/vib and normal) with both 2 inputs, with 2 band EQ on both channels, and a pair of knobs to control the vibrato (speed/intensity).
If you need to know anything more, please ask. I really hope someone knows the solution. I'm not really advanced with amp repair so please be easy on the tech talk.
Thanks in advance,
Tristan
P.S. I noticed in the schematics, there are 4x 12AX7 and 1x 6AQ8, but my amp has 3x 12AX7, 1x 12AT7 and 1x 6AQ8
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Try putting a 12ax7 in place of the 12at7. I won't hurt anything and might solve the problem.
I don't know much about tremolo circuits but I know a 12at7 is a lower gain tube than a 12ax7 so if the tube in question is for the tremolo that could be it. A lot of amps use a 12at7 in the phase inverter position though so maybe not.
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Thanks for your reaction!
Is it possible to switch one of the 12ax7's with the at7 to find out if it's solving the problem? Because I don't have another ax7 lying around.
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You can swap tubes as you suggest. It is better to have an extra around to swap in though because you are bringing in more variables by swapping positions of the other tubes. It still could be helpful though because if the tremolo is stronger when you swap you've probably found your problem. You just may not like the sound you get with the 12at7 in the other position; or you might like it - who knows?
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I've got an Elk Prosonic, similar amp, the trem should be deep- when I first got it I had to replace some caps to make it work. If you don't have much experience, and this is a tricky diagnosis, you might want to have a tech look at- Elk tube amps are similar in theory to Fenders but are wired on terminal strips. A good tech should be able to trouble shoot it, there are no expensive parts in that circuit except for the tube.
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> tremolo it is barely noticeable
Replace the electrolytics.
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First of all, sorry for my ver late reply.
I was hoping I could bring my amp to a friend of mine who has a lot of experience with amps and other tech stuff (used to be his work), but he didn't have time for me yet. So I wanted to wait with replying till I brought him a visit, but, yeah, I didn't. :sad:
So until then, I have one question left: with 'replace the electrolytics', do you mean, replace them with the same, or other values?
Oh and by the way, swapping tubes didn't do much.. So I guess the problem is in the electrolytics.
Also, thanks for all your replies, I appreciate it :).
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I have one question left: with 'replace the electrolytics', do you mean, replace them with the same, or other values?
Yes, if you can't get exact values, go a little bigger, not smaller, on voltage, its a must. OTOH, 47uf should be fine for a 50uf replacement but you can also use something a little bigger like say 60/65uf. Just make sure voltage raiting is the same or a little better/larger. In most cases (if not all),47uf to 50uf, either way up or down, you and the circuit wont know/hear the differance. Those two caps should be easy to find/buy, and not much $, maybe $1 to $3 each. Shipping will be more than the parts themselves.
As long as you know how to safely work on/in a tube amp, -- Just go for it! -- :wink: It's only 2 parts.
Hope this helps you, Brad :smiley:
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Both caps have less than 10V across them, use 10V to 50V replacements of same or up-to-double uFd value. NEGative to ground.