Shocking

[lowell]

Got a Premier 120R amp in for some repairs. It has a 2-prong power cord. When I connect my signal tracer GROUND clip to the chassis it blows the circuit breaker in my house. The chassis doesn't shock me however as before this happened I had been touching it with no problems. At one point when holding the grounding clip of my signal tracer I touched the chassis and was shocked pretty bad, blew the circuit breaker again. I am totally baffled by this. There seems to be 330VAC on the chassis with reference to earth ground. A: Where the heck is this high value of AC coming from? B: Why doesn't the chassis shock me when I touch it?? C: I'd like to upgrade this amp with a 3-prong, but obviously this isn't going to work with this problem.

[nickb]

Got a Premier 120R amp in for some repairs. It has a 2-prong power cord. When I connect my signal tracer GROUND clip to the chassis it blows the circuit breaker in my house. The chassis doesn't shock me however as before this happened I had been touching it with no problems. At one point when holding the grounding clip of my signal tracer I touched the chassis and was shocked pretty bad, blew the circuit breaker again. I am totally baffled by this. There seems to be 330VAC on the chassis with reference to earth ground. A: Where the heck is this high value of AC coming from? B: Why doesn't the chassis shock me when I touch it?? C: I'd like to upgrade this amp with a 3-prong, but obviously this isn't going to work with this problem.

My guess is there is a capacitor between live and the chassis - the cap 'o' death as they say. Not shown on the schemo since that's has been converted to a 3 pin plug. And that should be your first job. Yank the COD and safety ground the chassis with a three pin plug and cord. The transformer could be leaky, but less likely.
2) You get less of a shock because the signal generator ground is connected to safety earth so when you touch both the current goes through you -very dangerous . You are not so well grounded as the sig gen due to insulating clothes, shoes, carpet etc. Probably a quite a decent capacitance to earth though.

PS: Don't lick the chassis just to see...

[52 Bill]

Oh man, don't even plug that thing in again until you test the primary wiring and the transformer for shorts to the chassis.

The only reason you haven't gotten shocked before was the fact that you were not grounded.

[lowell]

Forgot to mention my first suspect was the death cap. I have already cut it out, didn't help.

If it were the primary shorted to the chassis then why 330VAC? It'd have to be a secondary wouldn't it?

[lowell]

Oh, and wouldn't the fuse blow if the PT was in any way shorted to chassis?

[nickb]

Forgot to mention my first suspect was the death cap. I have already cut it out, didn't help.

If it were the primary shorted to the chassis then why 330VAC? It'd have to be a secondary wouldn't it?

Oooo. I missed the 330VAC bit. If the live were leaking to the secondary HV winding that would do it. To open the the main RCD only requires a few mA - not enough to blow the fuse. Bummer. Looks like you might need a new tranny

[lowell]

Well whadya know, the PT primary to HV secondary reads 514ohms. :thumbs down: On the upside maybe I can buy this thing for cheap from the customer and fix'er up!

[lowell]

Unfortunately the schematic I posted is incomplete and these tubes are so old I can't read what they are. 6EU7, 12ax7 etc... and don't know what position they're supposed to be in. Almost positive they were in the wrong sockets when I received the amp. Anyone have a complete schematic or at least a tube layout? Thanks in advance.

Total filament draw, excluding the rectifier, for this amp looks to be 3.3A. 2x6v6, 6EU7, 6AQ5(EL90), 12ax7 (x5) is what I THINK is in here. Waiting on tube layout to confirm. If this is correct then Weber's Deluxe PT should be sufficient. It has the rectifier taps, 5A 6.3v tap etc... http://www.tedweber.com/media/import/w025130sch.JPG

Is the 6aq5/el90 also: 6HG5, 6005, AND 6669?

[lowell]

I just broke the news to the owner and he, very surprisingly, wants to fix it. He also said it was working before he brought it in, but one 6v6 was missing. I was surprised when he told me that, and I asked him if he'd ever been shocked by the amp and he said no. So I'm questioning my diagnosis. I have made sure that all 3 HV secondary leads are disconnected and completely unterminated when I measured 514ohms from them to the primary. This has to be correct, right? Is there something that I COULD be missing? I suppose it's possible that the missing 6v6 had shorted and caused the PT short, but can only surmise as to what, how, and when it happened. All I can do now is go by the readings I'm getting with the amp on my bench.

[nickb]

Unfortunately the schematic I posted is incomplete and these tubes are so old I can't read what they are. 6EU7, 12ax7 etc... and don't know what position they're supposed to be in. Almost positive they were in the wrong sockets when I received the amp. Anyone have a complete schematic or at least a tube layout? Thanks in advance.

Total filament draw, excluding the rectifier, for this amp looks to be 3.3A. 2x6v6, 6EU7, 6AQ5, 12ax7 (x5) is what I THINK is in here. Waiting on tube layout to confirm. If this is correct then Weber's Deluxe PT should be sufficient. It has the rectifier taps, 5A 6.3v tap etc... http://www.tedweber.com/media/import/w025130sch.JPG

I really can't help much. This guy (old eBay listing?) Vintage Mid 60?s Premier 120R 1x12? Combo, Jensen, Rare! Reverb Tremolo, Classic | eBay ???????

Claims the lineup is
V1- EL90 <<--can't be right!!
V2- 12AX7
V3- 12AX7
V4- 12AX7
V5- 12AT7
V6- 12AX7
V7- 12AX7
V8- 6v6
V9- 6v6
v10- 5Y3GT

Here is the Multivox Premier 120

With the leads flying and the RCD tripping, 514 ohms has to be right.

[lowell]

Thanks Nickb,

Is RCD residual current device aka circuit breaker?

By "has to be right" do you mean the PT is bad?

I dont think I can trust that dudes ebay listing

[olddawg]

It used to be illegal in my state to solicited customers for their broken gear. It could get your shop shut down back in the day.

[drewl]

It used to be illegal in my state to solicited customers for their broken gear. It could get your shop shut down back in the day.

Really?
I could see where that could lead to some shady behavior but I've had customers ask if I wanted to buy their basket cases for parts and even just tell me to keep it.

[Enzo]

That is different from you asking them. If you give them a $300 estimate, and they abandon it, that is one thing. But if you tell them it isn't worth fixing and could you buy it from them for $50, knowing you can fix it easily and sell it for hundreds, that has potential for abuse.

[nickb]

Thanks Nickb,

Is RCD residual current device aka circuit breaker?

By "has to be right" do you mean the PT is bad?

Yes, that is what I meant. It wasn't very well put.

I dont think I can trust that dudes ebay listing

Agree. It's all I could find.