question on a Framus Dragon Amp 100watt

[titan7]

I have noticed I am getting a very slight volume drop every once in a while. It doesn't go back up just a slight drop. the amp is about two years old. The only thing I can remember going wrong was running it for about 10 mins bedroom level with the head at 16ohm and the cab at 8ohms, I forgot to switch it over The amp plays and sounds fine other than this slight volume issue? Any suggestions? Power tubes?

thanks!

[pdf64]

Setting the impedance out by a factor of 2, especially at low volumes, won't be, or have caused, a problem.
Tubes are a consumable, you need a known good set spare so that you can rule out tubes as a cause of the issue. New manufacture tubes have got a short life before they sound flat, even if their measurable performance is still good. Especially if they are getting cranked at gigs.
Power tubes need to have their bias setting checked on installation ie the bias setting might need adjusting each time a set of power tubes is put in. Unless your tube supplier can guarentee consistancy.
Have you got a schematic for this amp? If so could you scan and attach it to a post here?
Have you ruled out dodgy leads, speaker jack sockets, guitar wiring?
Is the volume drop a gain reduction or a power output reduction ie does the tone get more or less distorted?
Does it occur at all gain and volume settings?
Does the amp have an effect loop, if so does putting a lead between in and out cure the problem? Peter

[titan7]

Peter, Thank you!

I uploaded the schematic. I will also check the tone again but from what I remember the tone did not change, it was only the volume. The amp's prior owner gigged with it I have not. It does have an effects loop, how would I make the connections you are referring too? Sorry about the dumb questions, this is my first tube amp. I will also run the amp on another cab tonight to see if I am getting the same issues.

[pdf64]

Thanks for the schematic, that's very helpful. Check the back panel of the amp for jack sockets labelled SEND and RETURN, these are your effect loop. Try plugging a lead going between them - problem solved? Peter

[titan7]

A speaker cable or guitar cable?

[titan7]

I figured guitar cord. Plugged one end into the send the other into the receive in the fx loop. Does not appear to be having the same issue? What's going on with it? Now I will try it again later with I have more time.

[pdf64]

You're right, a screened cable such as a short patch lead. The problem is that the Receive socket has a switch contact in it, which forces the signal path via the effect loop if there's a plug in it. When the switch contacts get dirty / degraded, the switch never closes properly, it thinks there's a plug in there. By plugging in a lead you can bypass the bad switch.
Either leave a short patch lead in there all the time, or get the socket replaced. You could try squirting some switch cleaner aerosol in there to clean the contacts and it might solve the problem for awhile, but it will likely reoccur at the most inconvenient time.
Peter

[cbarrow7625]

That's a really unique combination of circuit topologies in that amp schematic. I'm not familiar with it at all. Can you share some of your impressions of the amp. In particular, I've never seen that type of midrange circuit. How do you like it? How does it compare to a 'typical' midrange control as far as tone & feel?


The "deep" control looks very interesting as well. is it useful? Does it really fill out the bottom end? I can see it working well on the hi gain channel but I would guess it might muddy up the clean channel too much. Can you tell me about it?

Lastly, it's unusual to see that tone stack on a hi gain channel. Does it give you a really wide range of tones or are the controls really only useful from about 5-10 on the knob?

Any info would be great. Thanks for post ing the schematic!

Chris

[titan7]

Peter, are you saying it the effects loop receive socket switch that's dirty or sticking? I will try the contact cleaner. The amp was sitting uncovered in a garage for a while. I will continue playing it this way for a few days and see if that fixes the problem. Thanks for your help I wil let you know how this works out.

*** Any suggestions about my JCM 900, see thread below.


Chris,
The amp just rocks! That deep control has amazing range on all three channels. This amp has much more low end than my Mesa Dual Rectifier, but it will not get muddy if I turn it down. It's geared toward hi-gain sounds, it's a monster. There are some sound clips on the net. Here is a photo

[pdf64]

The switch contact is dirty/degraded. When there's nothing plugged it the switch contacts come together and close. If there's dirt or surface degradation then the switch never closes properly. As the amp was left in a garage awhile, damp will condense on all metal parts and oxides will form, damaging the plating on the switch contacts. You might be lucky with switch cleaner but the only sure resolution to this will be to replace the socket.
The rule is never to leave an amp where you wouldn't be happy to sleep yourself, repeated condensation cycles will cause similar damage throughout any amp - Peter

[titan7]

Peter, thanks! I guess it was not the power tubes after all! I played the amp again tonight for about 20 mins, no issue with volume dropping when I had the patch cord in the fx loop. I will try the contact cleaner spray and also maybe a q-tip with the spray on it?

Last dumb question. There is no way to determine which FX Jack is bad right? So If I want a permanent fix I need to have both of the FX jacks replaced?

[pdf64]

It's the RECEIVE socket. The most successful way of solving this without replacing the oscket is to open the amp up, get access to the socket body, cut a bit of strong brown envelope type paper about 2mm wide, plug a jack into the socket, flush the contact with switch cleaner, soak the paper with cleaner, slip it between the contacts, remove the plug and rub the paper backwards and forwards between the contacts, then plug a jack in again and flush it with cleaner.
Regards your jcm900, the only thing I could add to Enzo's advice is that there is a 3 amp fuse a little downstream in the B+ / HT supply, which might be mounted inside on a circuit board. It's possible this might be blown - Peter

[titan7]

Thanks Peter!!! I owe you a cold one

I will follow your directions. I will pick up the electic contact cleaner, I assume it's safe to spray into the Jack hole.

One the 900, I will look for the fuse. I believe it's the power tubes as the prior tech checkup in 7/07 said tubes need to be replaced. I just order up a new set of JJ Pre and Power tubes, I will have the tech put those in and check the rest of the amp.

[pdf64]

Glad to be of help. Don't go over the top with the spray, a quick 1/2 second burst, especially if it's from outside in, as opposed to working from inside chassis as described. If you are going outside in, after the squirt then insert and remove a jack plug quickly several times in succession, you need to get the contacts open while there's plenty of the cleaner sloshing around to loosen any dirt. Then repeat squirt and jack in / out, to wash the dirt off. Peter

[titan7]

Thanks again, I will spray it on the 1/4" jack and push it in and out. If that does not work I will take the amp out of the case and do as you have discribed. don't want to risk spraying frmo the outside in. I assume this stuff won't hurt the electonics? Any brand recs? I was going to head over to Radio Shack.

Thank you!!