Crate Vintage Club 50 VC5310

[timt]

First I'd like to state that I am trying to locate schematics for this amp, if anyone has them I would be grateful if you could send them my way.

Second, I have the following strange situation.

Everything on the amp basically works, I just did a bunch of "preventative' maintenance on it.
However, while working on it, I noticed that some of the resistor values just don't match up.

For example: I have the VC3112 schematic and it states that R60 & R61 should be 100ohm, the bands are brown/black/brown/gold as well... so last I check that should add up to 100ohm & 5% tolerance. R45 also is red/brown/red/gold which should be 2.1k. Well, that said... R60 and 61 are both around 50 and R45 is 2.6k? I was only taught one way of coding resistors and that way back in physics 2 though so maybe I missed something? A whole slew of others are like that.

Now my multimeter could also be horribly wrong but some new radio-shack 5.6k resistors are all reading around 5.5k on it.



The reason I bothered to check resistor values was a hunch that the power amp section or transformer may be off/going. I have brand new matched tubes in it and I can get the plates to glow if I crank it. Granted, it has no fan or air circulation and it throws heat like a toaster. One or more preamp tubes may be bad as well but even in a self-biased amp I'm not sure if that could effect the power tubes like this.


Any suggestions? I emailed 'enzo' on this forum as he seems to know a lot but I don't really want to impose on him out of the blue.

Thanks, Tim

[Garydean]

When measuring resistors you need to lift one side out of circuit, then measure. Measuring in circuit is not accurate. Most resistors even when new are not exact and can be off by 10% or more. If the output tube plates are glowing orange then your bias is off and should be corrected.

Gary

[timt]

Ah, forgot about that.

There was a rule about not measuring resistors in parallel circuits. it's been a while.

You're supposed to do voltage and current and compare it or like you said, take it out of the board.

Thanks Gary.


I am still hoping to find the schematics or stock bias information on the amp.
I'm putz'n through google reading up on biasing but I think with just a MM and a fixed bias amp... this could be time consuming.

Correct me if I am wrong:
Pin3 - Gnd is plate voltage
Pin8 - Gnd is bias

Then you just grab a chart or use the calculator on Weber's website and figure out what it needs to adjust to.

Unfortunately, this is fixed bias so I need to install a trim pot or keep replacing resistors till I am happy?

-tim

[Garydean]

Have you asked Crate for a schematic?
What is the tube line up in your amp?

[timt]

One request from exactly a year ago ( Dec 27, 2007 ) got this reply, and I quote: "I’m not sure which amp that is, can you tell me your serial number please...". I provided the info and received no response.

They picked up the phone and knew what it was when I ordered parts though and even promised to send the schematic but I haven't seen it. Truly strange in my opinion.

I asked again yesterday so maybe I'll get a different response?

It has 4 EL84 tubes and 4 12AX7 tubes.

2 EL84s per channel.
I -think- the 12AX7s are
1: chan 1
2: chan 2
3: reverb
4: PI

could be wrong though.


-Tim

[Garydean]

What does TP17 read in DC? Measure that to ground. What is your DC voltage on the plates, pin 7, of the EL84's?

[timt]

honestly not sure what/where tp17 is.
i think tp17 refers to the power supply output?
can you red to lead and black to chassis test that with a MM?

plate voltages are: 366, 366, 369, 369 (1-4)


not sure if there is still a problem now though.
the tube plates aren't glowing anymore and it's been cranked for 20-30min.

then again, windows are open and weather/wind are both great and back of case is off.
playing with the preamp tubes to try to get rid of the idle buzz too.

[Garydean]

sorry TP means test point. It may be a bare jumper wire on the board some where.

[timt]

Going by the Vintage Club 30 power schematics (as I don't have the VC50 yet but have read they're similar), I get 324V.


Honestly don't know if that is true considering it said TP17 is after the branch with C29 & R43 in parallel. That is right before it goes to ground though.

[Garydean]

TP17 should be reading in the area of -15.6VDC.

[timt]

I think the tp17 on the vc30 schematic is different then. It said -220 or higher voltage.
blah I wish crate had better customer service.

In any case, the power tubes aren't glowing like cherries now and i'm switching out preamp tubes to eliminate the buzz... sounds beautiful. I am debating now selling it now. I wish I knew why it suddenly stopped glowing though.

The clean channel sounds almost as good as my Mesa Maverick did before it the output transformer died.

[Garydean]

the VC30 and VC50 are different schematics. The VC30 is Self Biased and the BC50 is a fixed biased amp.
TP17 will measure the B-, to the EL34's as per the schematic of the VC5xxx.
TP17 on the VC30 schematic is the test point at the cathodes of the EL84's

Glad things are good for you now.

[timt]

By chance do you have any actual vc5xxx schematics? I've been looking all over for them. Still no reply from Crate either.

[Garydean]

http://www.blueguitar.org/new/schem/...ge_club_50.pdf

[timt]

You sir... are my hero.
I have been searching high and low for that.


I'll be checking TP17 first thing when I get home.

Thanks again!