My guitar amp is on the way out

Rocker

  sadly my self built Stinger [designed by Denis Cornell] combo amp is on the way out.   And I think this time it is terminal.  For a few months the sound has become 'more wirey' and 'jangly' and this sound cannot be dialed out using the tone controls.  The open G, B & e strings just don't sound like they should.  I replaced the valves with old but known good valves and this made no difference to the sound.

I built the amp over 20 years ago and have been proud to tell people that I had built it myself.  Luckily I have a Pignose to hand so I have something to use.  The Pignose is not a good pedal platform, I only use a few drive pedals and a reverb pedal, but at least I get some usable guitar sounds from it.

I am thinking of something in the line of a Katana, not much volume needed but the Katana has a number of useful or potentially useful sounds.  If I could get a small solid state power amp [up to 25 watts or so], this could take the place of the Stinger amp electronics and could be used with my POD 2 as a front end.  A powered speaker would or could do the same job.  All suggestions welcomed, thanks in advance.

Not feeling very happy as I write this.

Fingers657

Can’t you get somebody to sort your amp out and bring it back to life ?

Rocker

Fingers657 said:

Can’t you get somebody to sort your amp out and bring it back to life ?

Thanks for your reply but as it is a self build I doubt if anyone would touch it.  Besides here in midlands ROI I don’t know anyone who repairs valve amps.

ICBM

It's quite likely one or more of the electrolytic capacitors is failing - they typically have a lifespan of somewhere around 20 years, and although they don't normally fail straight away after that (some last fifty or more), the chances of one starting to go is not zero. There isn't much else in a simple valve guitar amp that fails over time, so there's a pretty high chance (although not certainty) that it's this.

If you built it yourself, you should be able to fix it. According to the schematic I have, there are seven electrolytics in it, four main filter caps and three cathode bypass caps. It's difficult to be sure, but if I had to guess from your description of the sound I would suspect the power valve cathode bypass cap first - this can often be caused by it being close to the cathode resistor, which gets hot, and heat is the enemy of electrolytics.

ecc83

Aha! It's a single ended EL34 amp! Yes, I am with ICBM, that cathode resistor is going to run bloody hot so if the cap is close to it? DEDID.

Do you have a multimeter and can safely make voltage checks? If so run them by us. Also suspect is the screen feed R to the EL34.

As IC says, valve amps tend to live forever unless there is a specialist part you can no longer get. Not so in this case. You can PM me if you want and I will do my best to help you over email.

Dave.

Rocker

Thanks @ICBM AND @ecc83 for your replies. I don’t have a digital multimeter that I would trust so, over the next few days, I will study the schematic and see if I can locate the capacitor alluded to by ICBM. I will contact you guys privately for components as there is nowhere here to get things like capacitors etc. 

The circuit board is fairly cramped and my eyesight is not what it was but I will get back to you both. Thanks again, you guys have given me hope that the amp could be got to speak normally again. 

ecc83

Rocker said:

Thanks @ICBM AND @ecc83 for your replies. I don’t have a digital multimeter that I would trust so, over the next few days, I will study the schematic and see if I can locate the capacitor alluded to by ICBM. I will contact you guys privately for components as there is nowhere here to get things like capacitors etc. 

The circuit board is fairly cramped and my eyesight is not what it was but I will get back to you both. Thanks again, you guys have given me hope that the amp could be got to speak normally again. 

Going to be tricky to get circuit conditions right without a meter Rocks'. Even a 10 quid analogue job from a car shop will do for valve circuits.

And PHOTOS! Need to see what you see.

https://www.amazon.co.uk/Analog-Multimeter-Current-Voltage-Poratble/dp/B0BKFSBZK6/ref=asc_df_B0BKFSBZK6/?tag=googshopuk-21&linkCode=df0&hvadid=641737618217&hvpos=&hvnetw=g&hvrand=602165093402270804&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9046156&hvtargid=pla-2105359955487&psc=1&mcid=7705f818582a38bd8be08f08c47557c4

Dave.

Rocker

I will see what multimeter I can get in our local town, the one I have was got from Aldi and while it works, I don’t trust the readings. I will do what you ask @ecc83 as soon as I can. Thanks again for your reply. 

Modulus_Amps

What does it look like on the inside, I worked on one for a customer and it was a mess full of bad solder joints, making fault finding and repair extra challenging.
I am sure there are techs that would look at it. Cyril Ryan at Audiotronix would have been the guy I would suggest but he is retired now. He might know someone else to have a look.

Rocker

Modulus_Amps said:

What does it look like on the inside, I worked on one for a customer and it was a mess full of bad solder joints, making fault finding and repair extra challenging.

Thanks for your reply @Modulus_Amps.  ;I am sure that you will think my build is as much of a mess as your customers is.  My defense barrister will argue that the amp was built years before there were online videos of how to build valve amps, online pictures of neatly constructed valve amps etc.  I don't recall ever seeing the interior of a valve amp prior to undertaking the construction of the Stinger.  I built it following the schematic and soldered the components on the 'wrong' side of the turret board.  But there again my barrister will argue that the amp worked more or less perfectly for nigh on twenty years.  It got used weekly and was transported a lot in my car.  

I still have the schematic for the amp and am willing to replace whatever might need replacing.  The Pignose will suffice for my guitar playing until the Stinger is back up and running again.

57Deluxe

out, or  out out?

JayGee

[Clickety click-click]

Aha…

https://www.aggh.net/discussion/index.php?topic=47812.0

…single ended class A with a single preamp stage and a single “make up” stage after the EQ - not a million miles away from my Ampmaker SE5a kit build. There’s not enough there for it to be really broken. 

Don’t give up on it.

Even if you end up throwing all the passive components away and rebuilding it from scratch (or throwing a few quid at someone handy with a soldering iron to do it for you) using the original transformers, sockets, pots etc it’s going to be cost effective to fix that...

ICBM

Rocker said:

I still have the schematic for the amp and am willing to replace whatever might need replacing.  The Pignose will suffice for my guitar playing until the Stinger is back up and running again.

If you've got the same schematic as me, my first suspect would be C13, which is the power valve cathode bypass cap, in parallel with the cathode resistor R15. If that cap has started to break down, the amp will be biasing itself much too hot, which tends to cause an edgy, metallic type of sound, as well as possibly visible red-plating (you may need to look at it in the dark to see it).

If that's not it, the second most likely is probably C15, which is the first filter cap and is hit with high voltage and a large inrush current on power-up. This is probably less likely because it's more likely to make the amp hum than sound 'wirey'.

It may simply be sensible to replace all of them - C1, C3, C10, C11, C13, C14 and C15. They're not that expensive.

Rocker

Thanks @ICBM, from your earlier reply to my OP, that became my intention. I removed the chassis of the amp today and as the construction work is ‘untidy’ to say the least, replacing the capacitors will be an interesting project. I intend to fit an IEC mains connection when the amp is apart as the permanently wired mains cable makes transportation more difficult than it needs to be. Thanks again for your reply. 

ecc83

Rocker said:

Thanks @ICBM, from your earlier reply to my OP, that became my intention. I removed the chassis of the amp today and as the construction work is ‘untidy’ to say the least, replacing the capacitors will be an interesting project. I intend to fit an IEC mains connection when the amp is apart as the permanently wired mains cable makes transportation more difficult than it needs to be. Thanks again for your reply. 

Can we not see it? The wiring cannot be any worse than those 'point to point' built amps people drool over!

Also, technically (and possibly legally) you are not qualified to work on 'mains side' electrics. I will say you would have to be pretty thick to get it wrong but that is my understanding. Does the amp have a mains input fuse? If not get an IEC socket with fuse drawer. If you get the amp working and fit the IEC connector I strongly suggest you get it PATted. N.B. The earth wire from the IEC must be Yellow/Green and attach to the chassis by a screw, crinkle washer and nut that does JUST that job i.e. not a handy traff bolt.

Dave.

Rocker

@ecc83, I understand your concern about me working on the mains voltage side of the amp but I am a [retired] qualified [time served] industrial electrician.  I understand 'that' side of the amplifier a lot more than the signal side.  I agree with everything you wrote about earth connection, your description is exactly how the amp is wired.  It has a panel mounted fuse and I have considered fitting an IEC mains connector for several years.  I know this is generally scoffed at by techs and others but I have a few decent quality mains cables in my hi-fi spares box and I would like to use one of them to power the amp. 

So don't worry unduly about this, I am not sure if the PAT requirement applies to the Republic of Ireland.  It might be,  I can ask in an electrical wholesaler when I am next in town.