Ampeg SVT CL export model fan problem

[tubeswell]

I have one of these that I'm in the process of resurrecting. (It had a problem with the bias sensor power supply, which I've managed to fix).

I'm not sure whether it should be a 117VAC or 220-240V model fan. The primary side schematic shows the fan wired between mains-neutral and one of (can't tell which) the primary winding ends on the power transformer. (The amp is a 2008 model amp made in Vietnam). The fan won't run when plugged into the fan plug (on the top of the big chassis). At this stage I can't tell if the fan is working or not because I can't get any VAC reading across the fan plug leads (J15 and J16 on the terminal board), no matter which setting the polarity switch is on. The mains fuses are both intact.

http://bmamps.com/Schematics/ampeg/A..._Schematic.pdf

The power comes on at the wall with the power switch on in standby mode, and there is bias voltage on all the 6550 gird socket pins (I haven't biased up the 6550s yet or plugged them in, because I want to get the fan working first. (The bias voltage reading was present on all socket pin #5s with all the pre-amp tubes - including the 12AU7 drivers - plugged in). The pre-amp tube filaments all light up and there is a good heater voltage between the heater socket pins (6.6VAC without the 6550s plunged in).

Would the fan be something to do with the operation of the relay (K1?) in standby mode? Does the amp need to be in full on mode for the fan to work? Seems off that I don't have any AC voltage between J15 and J16 on the main terminal board. But then again, there's tell tale signs that someone else tried 'fixing' this amp before it arrived to me. There must be a connection between J15 and J16 at the terminal board - because I get a 2R reading between J15 and J16 without the fan plugged in. But would the fan lead terminal clip have been put back in the wrong place by a previous tech? Should it be a 240VAC fan hooked up between J14 and J16 (on the terminal board)? Or will I cook the fan if I try this (if the fan is actually 117VAC)?

[MarkusBass]

You haven't mentioned what is your mains power supply. I assume it is 230V. In both versions of the amp (US and export) the fan is 117V. In 117V version it is connected between J14 and J15 (directly to the mains voltage), and in the 230V version it is connected between J15 and J16 (which is half on the primary windings of the power transformer). The drawing that you posted does not explain anything because the connections to the power transformer are missing. To switch the amp from 117V to 230V you need to switch the filament transformer, the power transformer and the fan. You get 2 Ohms between J15 and J16 because this is resistance of one half of the primary winding (and this is correct). I don't remember but I think that in 230V mode the fan is on when the amp is fully on. I suggest that you draw the power transformer connections (on the schematic that you posted) because it seems to me that there was a mistake on the official schematic (for the 230V version). But I don't remember whether it applied to SVT3Pro, or SVT-CL.
PS: you can always turn on the amp for a moment without the fan and check whether you get 115V between J15 and J16.

Mark

[tubeswell]

NZ is a 230VAC/50Hz mains cuntry. I couldn't tell how the standby switch was wired because of lack of schematic material - I can't locate a schematic for the PT primary side. (And I can't find a preamp schematic either). I didn't get any AC between J15 and J16 in standby mode, so I'll try it with the power fully on.

I take it that it should run with the power fully on without any 6550s plugged in? (That it won't try and go into auto shut down mode? or do anything funny like that?

[Leo_Gnardo]

NZ is a 230VAC/50Hz mains cuntry. I couldn't tell how the standby switch was wired because of lack of schematic material - I can't locate a schematic for the PT primary side. (And I can't find a preamp schematic either). I didn't get any AC between J15 and J16 in standby mode, so I'll try it with the power fully on.

I take it that it should run with the power fully on without any 6550s plugged in? (That it won't try and go into auto shut down mode? or do anything funny like that?

IIRC your SVT CL fan should be on as long as the power switch is on. And no matter if tubes are installed. Standby is accomplished in an odd way - by switching screen grid current on & off. Saves switches from being eaten up & works just fine.

[Jazz P Bass]

Here is the Chassis Wiring:

SVT-CL Chassis Wiring.pdf

And the schematic set:

SVT-CL.zip

[MarkusBass]

IIRC your SVT CL fan should be on as long as the power switch is on.

I'm not convinced that this is true. I think that this is true only in the US. In whole Europe, New Zealand and all other countries with 230V mains power supply it's not. Please take a look at the schematic in the first post.

Standby is accomplished in an odd way - by switching screen grid current on & off. Saves switches from being eaten up & works just fine.

I see it differently. The Standby switch provides mains voltage to the power transformer assuming that K1 relay is engaged (it requires that no fault is detected in the power amp). Please note that the heater, bias and +/-15V voltages are provided by filament transformer. The power transformer delivers only high voltages (and not bias, nor tube heater voltages).
So for the fan to work in 230V version the Standby switch must be on and K1 relay must be engaged (no fault detected in the power amp). That's why most probably the fan does not work at the moment (since the Standby switch is off).

Mark

[Enzo]

And this:
http://bmamps.com/Schematics/ampeg/A...y_Drawings.pdf

[Jazz P Bass]

Nice!

[tubeswell]

Here is the Chassis Wiring:

[ATTACH]38393[/ATTACH]

And the schematic set:

[ATTACH]38394[/ATTACH]

Thanks for this Jazz P Bass

Where did the 'Layout' sheet come from I wonder? Was this someone's tinkering- Or is it a factory tech bulletin?

Are the nose-to-tail 1N3070s || R8 really necessary? (Are the transients a functional problem?) (FWIW I'm fairly certain I saw D55 and D56 on the main board anyway, because I vaguely remember futilely attempting to test them with the diode-test function on my meter when I did the initial swoop of the main board after I took it out (before I clicked that these were nose-to tail diodes).

Did the .1uF between R47 and R49 get left out at the factory? (I don't remember checking that - I better go back and take a peek)