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HELP! - Fender Tonemaster knackered (?)......


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5/20/2000 3:55 PM
Ian Anderson
HELP! - Fender Tonemaster knackered (?)......
HELP!!!!!  
 
Okay, here’s the deal… I’ve got a Fender Tonemaster which has an intermittent fault.  
 
I can play through it at gig levels at rehearsals for maybe ten to twenty minutes, then the guitar sound stops coming through the speakers and an almighty ‘hum’ emerges instead, a bit like when you plug in an effect which hasn’t been grounded correctly (or at all), but probably worse.  
 
Looking round the back of the amp when this happens, the tubes are glowing ‘blue’, *not* red – bias is okay, it was set today on an oscilloscope using the crossover distortion method and actually sounds better than it did set too cold with a bit cross-over distortion, unsurprisingly.  
 
I’m at my wit’s end with ‘cowboy’ amp techs round here – anyone know a ‘good’ tech who know their stuff in the North-East of England (Newcastle area). I will drive elsewhere within the UK (within reason of course) if the person comes highly recommended and is worth the extra effort to go to.  
 
I’ve took this amp to two techs now and neither can fathom what’s wrong, but invariably, the fault won’t occur when they have it benched (just my luck). One told me the amp was fixed bias even when he had the schematic which clearly shows the bias pot and apart from that, it’s easily visible on the underside of the chassis – I don’t trust him, or his spurs. The other one is okay and seems to know what he’s doing, but can’t find the fault.  
 
I’ve got a gig coming up this Wednesday as well and will have to use that damn Marshall JTM60 which is okay for rehearsals, but not even a patch on the TM (as you’d expect).  
 
Anyone have any ideas? If you tell me what to measure, I’ll lend a DMM and measure the voltages if one of you kind gents here will explain how to do it, and what *not* to touch.  
 
 
… Ian
 
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5/20/2000 8:51 PM
Gus

A guess would be a bad connection that goes bad with heat and vibration. Ask them to tap the wire connecton solder joints etc when this happens(this must only be done by someone thats knows what the are doing and know how to be safe around High Voltage). I worked on a deville where the Bias trim pot would cause problems (the wiper would lift from the carbon track)
 
5/20/2000 10:39 PM
Max

Hi Ian!  
 
Try to ask Mark Simons at hot rooks.uk,he might be able to tell you where to get a good tech,he's in carlton nr notingham,and knows few old ee,and dave mann music,in notingham might be able to tell you too,he deals with hi fi valve amps.  
 
Best regards.  
 
Max.
 
5/21/2000 1:31 AM
Peter S

Ian,  
Sorry you're having such trouble, those are great amps and it's probably something really simple. I just wanted to comment on one thing. Your amp IS fixed bias. the adjustment pot means that it is an adjustable fixed bias amp. The term fixed does not mean that the amp is not adjustable but rather uses a biasing sheme that applies negative voltage to the grids of the power tubes. It can be adjustable fixed bias with an adjustment pot or non-adjustable with fixed resitors. this is opposed to cathode bias which is altogether different. A cathode biased amp obtain it's bias by making the cathode POSITIVE with respect to the grid by using a resistor in the cathode circuit of the amp to drop voltage. I'm telling you this because you mentioned that you didnt trust your tech. Well he wasnt lying to you about the amp being fixed bias, it truly is, and intermittant problems are impossible to sus out if the amp is not misbehaving on the bench. If you have other good reasons to mistrust him then so be it, however he may be a good honest tech, even if he does wear spurs. The problem with your amp could be alot of things.....since the tubes have the blue glow when it happens they are getting high voltage, so that eliminates your HT as the culprit. It may be a faulty preamp tube or a lose connection. Try tapping on the preamp tubes to see if the amp starts working again. You can try installing new preamp tubes and retension all of the tube sockets first. intermittant problems are a techs worst nighmare.Good luck. Make sure you discharge your filter caps before attempting anything.  
 
PS
 
5/23/2000 12:46 AM
Bob

Thank you, Peter.  
 
P.S. I saw a tech riding an SVT down the 405 in a cloud of dust! Hi-Ho silver mica!  
 
Bob
 
5/21/2000 11:27 AM
Liam

Ian,  
 
I can recommend an excellent amp tech, but he's at the other end of the country. Whitstable in Kent to be precise. I can't recommend the guy too highly, never had a difficult to find problem where he couldn't come up with the goods.  
 
If you want to send him the amp, or are willing to drive down, email me and I'll give you his number.  
 
Liam
 
5/21/2000 2:23 PM
Ian Anderson

Thanks to everyone for the replys. I had it benched yesterday at a repair shop and we tried tapping everything for loose connections for an hour and a half.  
 
Unsurprisingly, I then took it to rehearsals and the same thing happened within 20 minutes when playing loud.  
 
About the tech I said I didn't trust (jingle, jangle - spurs/cowboy) - he just ripped me off last time he did my amps overcharging way in excess of the other techs in shops had previously. He really milked the situation to the full and was a right, well I'll refrain from bad language on this board, but you get the idea.  
 
Liam, I'll email you for that tech if I get stuck - just Kent is a hell of a long drive.  
 
I'm trying the Audio Brothers in Darlington first as I had one of their Hiwatt amps and was really impressed at the quality of workmanship.  
 
Anyone had any dealings with Arbiter (UK) with regard to repairs?  
 
 
... Ian
 

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