Ampeg CL Heaters but no lights

[bhssm]

Hi all,
This is my first post here and I want say how much I appreciate the depth of knowledge available here.

My problem is an ampeg classic is not powering up fully.
I'm getting heaters on all tubes but no power lights or no plate voltage.

I have checked all the obvious things I can think of, fuses, mains power etc. and there is no obvious signs of burnt or blown parts. Im getting full voltage up to the power switch but that is as far as I've gotten so far.

Any advise on how to proceed further would be greatly appreciated.

Thanks

[Sneakypete]

You need to be careful here - electricity can kill! Taking it to an experienced tech would probably be best but if you know there's no plate voltage does that mean you've checked the big capacitors in the power supply section and found no DC voltage across them? If so that would point to the rectifier (AC in DC out) or mains transformer. Take it to a tech if in the slightest doubt about what you are doing.

[Jerrold Tiers]

yes, unless you ARE a tech, it's best to take it to one.

Sounds like you are gonna try to fix it anyhow, so......

Assuming the standby switch is set for proper operation.....................

The question is whether you have voltage on the main power transformer primary. if not, you won't have plate voltage, obviously.

If you DO have voltage there, and it is wired right, then either there is some open circuit on the secondary side (bad part, loose wire, etc) OR the power transformer is actually bad.

bad transformers are rare.

[bhssm]

Thanks for the replys.
No DC on filter caps or rectifier. So It's down to the power transformer.
I'm assuming the secondary and primary taps are connected to the Jumpers on the AC line in board. I have the 240v version and I'm a little unclear by looking at the schematic I have which wires are what. Any suggestions?

[RickenBoogie]

I'd still take it in to a tech, unless you have all the test equipment, and are a qualified amp tech yourself, which is still unclear.

[bhssm]

I'm not a qualified amp tech, more of a burnt parts finder trying to learn. I do have a good quality DMM, dummy load and scope at my disposal. I'm also fully aware of the lethal voltages inside these amps. At this stage I am still determined to try to get to the bottom of this problem myself and hopefully learn a little more on the way.

So my next step is to ascertain the condition of the primary and secondary sides of the power transformer, but I'm still unsure of which connections leading from the transformer to the AC line in board jumpers to test.

[B-string]

Originally Posted by bhssm

I'm not a qualified amp tech, more of a burnt parts finder trying to learn. I do have a good quality DMM, dummy load and scope at my disposal. I'm also fully aware of the lethal voltages inside these amps. At this stage I am still determined to try to get to the bottom of this problem myself and hopefully learn a little more on the way.

So my next step is to ascertain the condition of the primary and secondary sides of the power transformer, but I'm still unsure of which connections leading from the transformer to the AC line in board jumpers to test.

The schematic should have wire colors from the transfomer. With a 220volt trans you probably have two primary windings (in series for 220v operation).

Ask Jerrold Tiers nicely he may have the schematic if you don't.

I would recommend doing resistance checks first with your DMM before any live voltage checks.

[Jerrold Tiers]

Since you have a 240 version, the primary windings will consist of two 120V windings in series (there are taps allowing finer changes , but don't sweat that for now).

The Standby switch feeds the main transformer, the power switch feeds the filament transformer and the standby switch.

The primary will be wired such that one wire is on mains, two are connected to a pair of tabs that are just connected together (and will also feed the 120V fan) and the last of 4 wires goes to the opposite mains. There will be some extra wires that are unused taps.

I have schematics and board layouts in PDF, so PM me an email, I'll send the info, and we'll sort it out.

While you are at it, find the main power transformer part number. it will be "94-XXX-YY" where the Xs and Ys are numerals. I may have the transformer info also.

[B-string]

Could I mail you a blank DVD one of these days JT? I keep thinking my repair days are over, but the word is out in this little slice of paradise (LHC).

[bhssm]

Thank you for imparting your knowledge gents. That's exactly the information I required.

Jerrold, I will PM you when I get back to the bench on Monday with the main power transformer part number.

Cheers!