Laney VC-50 probs

[Dronno]

Hi All.

New here :C

I have a VC-50 which has been great for over 5 years but has just started to give some grief with the 2nd channel. Probably my fault, I was a bit rough with it on a small step (about 1 inch drop, I was in a hurry and just pushed it off) I thought about this afterwards and well, yep, idiot.

I'm not sure if that is anything but hey?

I've had valve amps for over 25 years, and I don't beat around my old Marshalls. I guess I took her for granted and now I'm sorry.

Anyway, the level from the 2nd channel (Channel A, dirty) is almost non existent. You can just hear sounds like it's turned right down, though it's on 10. (It's a Laney, doesn't go to 11)

I've swapped out all the 12ax7s in the amp to no avail. I'm about to start going over the schems when I thought I'd see if anybody else might have some ideas.

My thoughts: Obviously the power section is fine. I believe the pots are fine, coz when I turn them down the little bit of noise goes away altogether, The relay seems to be operating, but perhaps there's an issue with the contacts in it? I've just got to go over the signal chain of that section of the pre amp!

BTW, I am an electrician, which means I don't know much about electronics, though I should be able to not do the funky chicken with this.

All help gratefully accepted.

Thanks.

Dronno.

[Chuck H]

Do you have a schematic you can post?

That amp has what looks to be an elaborate effects loop system. Make sure the effects loop is being managed properly for the intended operation. Maybe a switch was flipped or a level adjusted accidentally.

With the effects loop in "insert" mode, try putting a jumper in the effects loop for the affected channel. Could be a dirty jack switch.

Also, try plugging the affected channel "send" into the working channel "return".

Then, try plugging the working channel "send" into the affected channel "return".

Make sure the effects loop is in "bypass" mode with the jumpers removed.

How do you usually use the loop/s? did you remove or change your effects unit without changing other settings?

Report back.

[Dronno]

The VC-50.

Hi Chuck.

Thanks heaps for that advice mate, I will try it asap. I don't think it is the issue, but you never know. The reason I don't think it is the issue is this. I was probably wrong in saying it was channel 2. It is essentially a 2 channel amp. BUT, each channel effectively has 2 channels, so when I say channel 2, I mean channel 1, dirty, lets say. In my familiarity with this thing, I call them channels 1,2,3 and 4.

Ok, so 1a is a single master volume. 1b is a pre and a master, 2a is a dirtier pre and master, and 2b is the same pre and master as 2a, plus a cascaded gain stage adjusted by a 3rd knob. Kind of like adding a tube screamer in front. It's a little hard to use but you can generally dial it in. All these are selectable from foot switch, along with reverb. Channels 1 and 2 have independent fx loops, with separate returns, as well as a common return??? and also an overall loop which has a volume control, which I use as an overall master by jacking it. A little trick I learned on the various forums. Otherwise, you have all your settings just fine and then someone says turn up, well then you have to gin around with 3 different masters.... This way, just the one on the back. Some move them to the front, which I might just do.

I've uploaded the schems I found. I'm gonna print them and start colouring in....

I'll give you a little of our history here.

The VC-50 came into the fold around 2007. I woke up one morning and there was an email saying I owed so and so $650 for this amp. I did this a lot back then, bought a '62 Jaguar and 25th Anni Strat the same way. It was a fairly dire sound stock, the original speakers are famously shrill. I scored some '61 Jensens but they didn't work, very in-efficient, was like playing a 10 watt amp. Then a friend of mine gave me a pair of green backs. these things are pre rola, and stunning. One has a little bit of a grind inside, but barely noticeable. Also, i discovered these Sovtek 12AX7BP's, they have phenomenal tone. Also, a mate gave me some boogie EL34's, on a 6L6 base, but either will work in this one.

So with those enhancements, she has sweet tone. Jack in the back, Greenbacks, Sovteks, and boogie power valves.

As mentioned, I've been playing with a 100 watt marshall SL since 15. I just took the SD convertible 60 in for service that i was running before the Laney.

So my amp herd:

1973 M Superlead on 4x12 ri basket weave cab (green backs)
1974 M Superbass on 4x12 ri basket weave cab
1984 F Concert 2x10 (I put in Jensen Alnico's)
1986 SD Convertible 60 1x12
1993 L VC-50 2x12 (with the green backs)

I just say all this so you can see I been ginning around with valve amps since '85 and my pursuit of tone. Bought the 73 SL for $600 back in the day.

Well cheers mate. I really would like to fix this one on my own, the others I could have had a crack at, but I think my sanity will cost more to fix than the amps should I even try .

OK, so I'll print the schems and try and hi-lite the path around the offending stage.

Thanks mate.

Robert.

[Dronno]

A quick update.

I got into it with the DMM. I don't seem to have all the same components, or maybe they're off somewhere else??? So I got some readings.

I measured from ground to each leg of R-11 (330 and 180V DC), R-15 (348 - 199) R-19 (350 - mV) and R-17 (mV - mV). The drawings say that the low side of R-19 should read +210 V. So possibly theres a dry joint there, or a cactus resistor. So with the dmm on impedance, I get OC. So I'll start by replacing that resistor.

I'll let you know how I go. Being sunday, I might have to chain a resistor together. Be plenty of watts then! (I mean for the 1/2 watt resistor, only expect 50 at the 2x12's, don't want to fry em!)

Cheers.

[Jazz P Bass]

A Cactus Resistor.
I like that

[Dronno]

Oh-oh.

Ok, so the electronical shop is shut. So I put together 4x 22k and a 12k. Reads right on 100k on the dmm. As a test run, I hook the ends around the on board resistor. Now I whack the impedance again, coz 2x 100k in parallel isn't 100 k anymore. So it Round 97 k. Cool. Now the fiancé is nursing the flu in the room accross the hall and I flick the standby. Anyway, it starts making all the right sounds, at around 50 watts and she's slamming the door but the amp seems to be working!

Would have been cheaper sending it out as now I gotta buy chocolates and flowers and maybe even some counseling....

I'll do a proper fix and when I can, plug in and see how she goes.

[Dronno]

Ok, replaced that 100k resistor, all good. Thanks for all your help guys.