I have occasionally seen grid-leak resistors cause that kind of frying noises. You wouldn't think so because there's virtually no voltage/ current going through them, but it can happen.

@vintageguitaramp_guitarteacher

2 ай бұрын

hello. Thinking about it. I was struggling to get a reading on one of the 1 MEG grid leak resistors. I did get a reading eventually. I wonder if it's gone bad. That's the first port of call. Take care.

@goodun2974

2 ай бұрын

@@vintageguitaramp_guitarteacher , The current going through that first triode, and perhaps the second triode as well, is probably varying all over the place. You might not be able to measure it as fluctuating voltage on the plate resistors but perhaps if you put a milliameter or microammeter in series with the plates of the triodes you will see it fluctuate. Or take a look at it with the O'scope ( I'm a piss-poor scope jockey and I always hated it when somebody would say that to me!😉). Maybe try putting a relatively low value resistor, 2.2 or 4.7 k, in between the plate supply of the 2 triodes and add another 10 to 20 microfarads of filtering to ground for the first triode.

I whole heartedly agree with your and the owners forward plan on this amp. I have really never seen the point of maintaining originality if the amp don't work. Looking forward to hearing the end result. It'll probably be the first Selmer Little Giant that sounds usable I recon. Before you ask; Yes I did have a brand new one in the 1960's and quickly traded it in for a Watkins.

@vintageguitaramp_guitarteacher

2 ай бұрын

Hello Pete. Yes, I agree. It's pretty useless as it is. I wasn't going to ask lol. Ah, good lad. I'll let you off then :-)

Firstly, 10M to ground is called "grid leak" bias. It's a cost cutting measure - saves on the cathode resistor bypass capacitor. Second, if operating the guitar pot is that scratchy then most probably the input capacitor is leaky and feeding d.c. back to the guitar.

@vintageguitaramp_guitarteacher

2 ай бұрын

Hello. This a MK three. The grid leak is 1 Meg. I changed the input cap as I said in the video. It made no difference. I am going to rewire it to cathode bias. It's easy to do it and will be much better. Take care.

I remember seeing those in the Selmer catalogue back in the mid 60's, mains lead looks pre 1970's colours of Red, Black & Green when they changed to the newer colours.

@vintageguitaramp_guitarteacher

2 ай бұрын

Hello. Yes, the guy bought it from the catalogue in the early mid 60s. It's still in good nick but we need to work on the sound. Take care

Hi Martyn, remember drooling over one of these, when I was a bit younger! Then obsessed over a Watkins westminster that a mate of mine owned, that was before owning any decent amps. Did own a watkins rapier 33 guitar though! That amp needs a serious tweaking, by the sounds of it.

@vintageguitaramp_guitarteacher

2 ай бұрын

Hello Steve. The amp looks great but it sounds terrible. Part two will be coming soon and I have a few ideas to sort it. Those Watkins Rapiers are getting quite valuable now. Take care mate.

Looks like a radio!

@vintageguitaramp_guitarteacher

2 ай бұрын

Hello Chris. It sounds like a radio at the moment; on medium wave! Take care.

I had one back in the 60's lent it out and never saw it again The guitar I used was a Framus cello (arch top )guitar with an adjustable Eagle pup which I still have

@vintageguitaramp_guitarteacher

2 ай бұрын

Hello Frank. Isn't that the case. How many musicians have lost gear through being generous. It's nice that you still have the old Framus though. Thanks for watching and take care.

Try a different 12AX7 and see if the DC leakage into the guitar is minimized. As for the hum that shows up when you turn the tone control down, that may be a sign of an impedanxe mismatched where the circuit is being loaded or unloaded by the design of the tone circuit. The other thing that injects hum is having an on-off switch on back of the tone control or volume control instead of a separate power switch where the AC is kept away from the signal carrying parts of the circuit.

@vintageguitaramp_guitarteacher

2 ай бұрын

I have already tried a different 12AX7. That didn't make any difference. Yes, the hum could well be due to the on off switch. That's the schematic: www.vintagehofner.co.uk/britamps/selmer/schematic/lgmk3.html It's a weird circuit

@goodun2974

2 ай бұрын

@@vintageguitaramp_guitarteacher , I can definitely see why the tone and volume controls would be highly interactive and change the load impedance between the two halves of the 12AX7 depending on how they're set (assuming that this schematic is correct) and also because there's no R-C decoupling between the triodes. Also worth noting that there's no screen resistor on the EL84. Hum reduction might be improved if you disconnected the heater-winding centertap and installed an artificial center tap with 2 resistors from the heater line to ground, or better yet, wire the common tail of the balancing resistors to the cathode of the EL84 and thereby bias up the heater supply above ground. It also goes that without saying that any common grounding of input jacks and so on to the metal front plate needs to be cleaned and tightened.

I had one seemingly identical to this one it cost me Twenty Quid from a store in Romford. With a Burns Sonic with both Trisonic pick ups on in series they did a very good low volume version of Eric Clapton on the Bluesbreaker album. I've never seen one on this side of the pond...

@vintageguitaramp_guitarteacher

2 ай бұрын

Hello. I guess £20 was quite a lot of money in those days. They are quite rare in the UK now. Sadly, this one does not sound good. In part two we rewire it in to a 5F2-A. It sounds much better now. Thanks for watching and take care.

Carbon comp resistors can drift with age as I found out

@vintageguitaramp_guitarteacher

2 ай бұрын

Hello again. Yes, they are all a good bit on this amp. Take care.

My first amp

@vintageguitaramp_guitarteacher

2 ай бұрын

Hello Jerry. How did yours sound?

@jerrypinner1671

2 ай бұрын

@vintageguitaramp_guitarteacher it's a long time ago - but it was the first I found out what a guitar through a dimed valve amp sounded like- warm harmonic overdrive- really great.

@jerrypinner1671

2 ай бұрын

@vintageguitaramp_guitarteacher long time ago- great, it really rocked, loud enough to upset my parents! Mine came with a Selmer soft cover- it was like new

Sounds like a resistor. And/or tube rustle.

@vintageguitaramp_guitarteacher

2 ай бұрын

Hello. Yes, could a grid leak resistor. Take care.

Is that a MK1 Martyn, there are differences in where the tone volume circuit and values to the MK3?

@vintageguitaramp_guitarteacher

2 ай бұрын

Hello. I think it's a Mark two. Someone had hand drawn a schematic of the Mark two and it was much closer than the Mark Three. It needs some work but I have ideas. Speak soon mate. Take care.

@electrokatt2246

2 ай бұрын

@@vintageguitaramp_guitarteacher ah right, `I`ve not seen any schematics for that one, ,late 60`s?

Changing the screws will rob tone 😐

@vintageguitaramp_guitarteacher

2 ай бұрын

Hello. It doesn't have any tone.