Bare Knuckle Pickups Forum
Forum Ringside => Guitars, Amps and Effects => Topic started by: Twinfan on December 31, 2006, 12:04:44 AM
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I was checking my 60w Klipp head out earlier today and removed/reinstalled the two power valves. When I powered it back up, the output was very crackly and faded in and out a bit. The right hand power valve glowed REALLY bright orange and the other looked normal. I swapped the valves for another pair and got exactly the same thing - the right hand valve seemed to overheat.
What's the likely problem? Damaged valve socket (left) causing all the voltage to go to the right hand valve? Please tell me it's not the output transformer as it's still got the original Partridges in there...
Is it going to be expensive to fix??????
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Hi Twinfan,
Sorry to hear about the amp. The most likely culprit(s) are the bias resistors having eventually burned out over time on the base of one of the valves. This is quite natural with an older amp. Indeed many 'classic' amps get their unique sound from the fact that many resistors and capacitors have degraded with age.
If any of the resistors (large carbon or wire wound) were to fail due to old age, this would have the effect of sending the bias across the output pair right over to one side, leaving one valve hard on and the other running cool.
Bias resistors age over time, albeit a lot slower than several sets of output valves. They are however cheap to replace.
Switch off the amp and allow a little time for the large electrolytic power supply capacitors to discharge. Remove the valves, and look on the underside of the valve bases, ( I assume the KLIPP is old school hand wired etc). If not, just look for the larger resistors leading off from the base pins on the PCB.
On one valve, you should find a burnt, open circuit, or even abnormaly high resistance resistor(s) compared to the output valve bias components on it's mirror image on the other valve.
If you are fortunate, the undamaged set of components will give you the colour codes/ resistor value(s) and types you need to buy from 'Maplin' to repair the other side.
This advice is not meant to replace the attentions of a 'hands on' tech, but when I was repairing them (many years ago) the above would be the first thing I would look for.
The consolation is that if your output transformers had 'gone' - you would probably have had experienced the acrid smell of burning transformer winding insulation and blasted output fuses.
Regards,
FF.
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Fourth Feline - you are a star my friend :D
I'll drop the amp off at my local place on Tuesday and have them check it out as I'm not going to chance frying myself! There was no burning smell or smoke, so your sugestion sounds like it could well be the problem. Phew! The Klipp is hand wired as you say, so it should be a simple, and hopefully cheap, fix.
Thanks for setting my mind at rest!
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Hi Twinfan,
Thanks for your reply, I just hope that my assumptions prove to be correct in this case.
Please let me/us know what the outcome was ! :D
Regards,
FF.
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If it's not what 4th Feline said, it could also be the output transformer. Hopefully it isn't cause that's an expensive repair job.
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What makes you say that Ratrod? How would it make one valve run WAAAAAAAY hotter than the other?
It'll be going to my local shop tomorrow and they should turn it around in about 10 days.
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My amp had something similar. One of the power tubes was glowing like a lava lamp. It was caused by a short circuit in the output transformer.
I don't know how or what but this is what the repair man said.
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Oh no - I hope it's not that!
<Crosses fingers and hopes for the best>
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Hello again Twinfan,
I unearthed the circuit diagram for my 50w Laney LH50R -II and had a look at the configuration of the output transformer. Unfortunately I can see that under certain circumstances the output transformer could be faulty enough to drive one valve harder, yet not blow an output fuse.
As a general rule, the transformer on a 50-60W (2 output valve) amp has a three wire primary winding. The 400volts comes off the mains transformer into the centre of the primary and then the anode voltage for each valve is fed off each end of the same long winding. If the coils of the primary between the centre tap and one end tap only shorted together part way along the line, the resulting feed voltage to the valve at that end of the transformer primary would change dramatically in relation to the other valve feed. In other words, the 'centre' of the transformer's primary winding would be effectively moved off to one side etc.
I am just surprised that the resulting breakdown in insulation did not make the transformer give off at least some melting shellac/arcing smell . This could be because it happened very quickly and made an instant contact at the 'new' point, avoiding arcing etc.
It also looks like Laney run the valve cathodes straight to earth, thereby removing the hope that a cathode bias resistor may have gone faulty. There are still the two grid bias resistors to consider (and hope faulty), but I fear the worst if your "Klipp" is wired like my LH50.
I cross my fingers and await with baited breath...
Regards,
FF.
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Oh no :(
If it helps, here's a circuit diagram for a Klipp 100w:
http://www.drtube.com/schematics/laney/klipp100.gif
If the transformer HAS gone, what's a good replacement to consider?
Is there still a chance it could be a faulty valve socket? I know they're prone to issues on the Klipp amps?
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Hi Twinfan,
It is the same basic circuit as the 50/60 types, except in a 100/120w version the power output valves work in pairs, the top pair in parallel with each other and the bottom pair the same. This in effect makes two 'super' valves.
For this reason in a Fender "The Twin" (where the bias is externally adjustable from the back panel) one can drop out the inner two valves and re-bias to get through a show on half power.
As for replacements, Laney would probably have to provide that, or at least their very helpful technical department could confirm the voltage input/ output requirements of the transformer, so the damaged transformer winding may be rewound by a local firm that can do that kind of thing.
I would confer with Laney technical dept by phone on this one, as they will advise as to cost and availablity whilst probably being best able to re-wind if not replace their own product.
Still a worthwhile price for a classic hand wound amp though, and an assurance that many years of hard use can be relied upon from hereon in.
Based on my contact with them, I feel that if any company will charge sensible prices and deal with you in a down to earth way, it would be Laney.
All the best TF.
FF.
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Hi Twinfan,
It is the same basic circuit as the 50/60 types, except in a 100/120w version the power output valves work in pairs, the top pair in parallel with each other and the bottom pair the same. This in effect makes two 'super' valves.
For this reason in a Fender "The Twin" (where the bias is externally adjustable from the back panel) one can drop out the inner two valves and re-bias to get through a show on half power.
As for replacements, Laney would probably have to provide that, or at least their very helpful technical department could confirm the voltage input/ output requirements of the transformer, so the damaged transformer winding may be rewound by a local firm that can do that kind of thing.
I would confer with Laney technical dept by phone on this one, as they will advise as to cost and availablity whilst probably being best able to re-wind if not replace their own product.
Still a worthwhile price for a classic hand wound amp though, and an assurance that many years of hard use can be relied upon from hereon in.
Based on my contact with them, I feel that if any company will charge sensible prices and deal with you in a down to earth way, it would be Laney.
All the best TF.
FF.
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Thanks FF. The amp has gone to a company in Liverpool for repair via my local music shop. They're called "GEE Electronics" and I believe they have a very good reputation for valve amp repairs.
Will a new output transformer (if required) drastically change the tone of the amp?
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No, the output transformer serves a fairly utilitarian current transfer function and to provide the same voltages, they will have to use the same ratio/number of windings.
The crispness or squashiness of power transfer should therefore remain the about the same. The only variable can be if they use a different size 'former' on which the windings are mounted. Even then, it is not a solid state/ valve type of difference in sound, more a subtle change in power output.
FF.
p.s I have sent a PM off topic. :D
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Thanks for the reply FF. I've asked the repairers to call me before doing any work so I can check what they do. I'd be gutted if they binned a repairable Partrdige transformer!!!! I'm still crossing my fingers that it's something really minor...
I'll keep an eye out for the PM (not arrived yet...)
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Good idea to keep an eye on the repairer, however reputable they might be. They may think "replace with a lesser specification transformer rather than have a re-wind on the Partridge, just to repair it quicker and therefore 'please' you"...
The P.M. ( we may as wll do it here )
was about just what string types/gauges and picks you use. As a fellow S.G. user, but with a different playing style/tone, it's Stormy Monday's and D'addario 10-52 with a BKP 1.21 celluloid pick.
I therefore curious what works for you and your Riff-Raffs/playing style.
In guitar magazine interviews, Angus seems to be using EB 9-42 and a heavy pick, but on guitargeek.com they say he uses 10-48 !
FF.
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My Angus setup is:
Epiphone ’65 reissue SG with Maestro Vibrola (Korean custom shop limited edition) fitted with:
o Riff Raffs
o CTS 500k audio taper potentiometers
o Switchcraft jack and selector switch
o Hovland MusiCap capacitors
o TonePros bridge
o Tusq nut
o Dial pointers
I use 1.14mm Jim Dunlop Ultex Standard plectrums and Ernie Ball Regular Slinky strings (10-46).
At our last gig, a punter told me I had Riff Raff nailed (both playing and tone-wise) so I guess I've got it right!
I believe Angus uses both 9 and 10 gauge strings for recording - 10's with a 48 low E for rhythm and 9s for solos. Live, it's 10s if his hands are not too knackered (he has tiny hands!) otherwise it's 9s.
I find 9s on a 24.75" scale length too sloppy, so I stick with 10s for a bit of "fight". Works for me, and you get a fuller tone. Combined with the Klipp my sound has a bit more ooomph than Angus', but no regular punter would know any different. Some of the guitar players can't believe I'm using a "cr@ppy old Laney" though... :lol:
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An update on my faulty Klipp:
Just had a call from my music shop and the amp will cost £90 to fix. The repairers hadn't said exactly what the problem was but I'll find that out when I get the receipt for the work. At that price nothing major can have gone wrong so it must just need the odd minor component and a service. Phew!!!!
I'll update this thread with the parts repaired/replaced after I pick the amp up.
And relax........
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Hi Twinfan,
May I be the first to congratulate you on the good news ! I look forward to hearing what the exact cause was, so I can go back and relate it to the circuit diagram you kindly posted.
* OFF TOPIC*
Thanks for the Angus Young info by the way, I also went for the CTS 500k pots instead of the stock Gibson 300K ones. The only difference being that I had to go for linear taper volume controls to match the sweep of the old ones (as per a previous thread). I fitted Sprague orange drop caps, as I had not heard of the Hoyland at the time. I am convinced they do make a difference though, as I replaced them before the pots or pickups and heard a silky sweet clarity not there before.
FF.
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Cheers FF - I'll let you know what the amp issue was.
Re. the Angus stuff, I used Sprague Orange drop caps before the Hovlands and they were good value. Nice and clear and a decent price. The Hovlands are more expensive and just have that bit more musical edge to them. There's not a lot of difference though to my ears, to others it may be much more.
For the pots I've been very happy with the audio taper volumes. I roll down to about 7ish for rhythm playing and up to 10 for solos. Works for me!
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Just picked my Klipp up from being repaired. £89 - not bad at all.
The problem was a faulty valve base socket that was repaired, plus the amp was given a general service check too.
Thought some of you (FF mainly) might be interested in the result!
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Thanks for the information Twinfan, please ignore my private message about the same subject.
Good deals all round eh ? :D :D :D
FF.
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Just picked my Klipp up from being repaired. £89 - not bad at all.
The problem was a faulty valve base socket that was repaired, plus the amp was given a general service check too.
Thought some of you (FF mainly) might be interested in the result!
£89 to replace a valve base and a general service - I've got to put my prices up.
I've just modded a Marshall Bluesbreaker that required removing the PCB from the amp. also included a pair of 6L6s in the deal and a general service. total cost... £70
Getting repair bills like that is why I taught myself about valve amps - ripoff techs boil my piss :x
:twisted:
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Well my local shop will take a cut as the middle man, so I guess the repair itself was £80ish? Saved me a trip to Liverpool anyway!
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Glad things worked out OK.