Foreplay III help request

TimH · 3561

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Offline TimH

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on: April 06, 2012, 03:42:45 AM
The resistance check looked OK.

Here are my problem voltage readings:

power transformer  terminal 4   1.7 VAC

power transformer terminal 5   1.7 VAC

H1    5.0 VDC

H2    1.5 VDC

21    -5.0 VDC

Thanks



Offline Grainger49

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Reply #1 on: April 06, 2012, 05:02:55 AM
Tim,

I have never heard of a Bottlehead transformer being bad out of the box.  As a matter of fact, you have to molest them pretty well to damage them.  The fuse should always protect the transformer.

So, I mean don't worry about the transformer on those readings.  Check from transformer T4 to transformer T5 and see if you get ~6.3V AC. 

If not there is something dragging it down.  Check the orientation of the capacitor and the diodes.  They can be a booger to get right.  I've been doing this a long time and I get one backward every so often still.

Let me get this right, the only voltages that are off are the ones listed?  Right?  If so you are reading wrong.  If the downstream voltages, say T1, are good then it is just a problem reading the early terminals.

Terminal 21 is connected to the cathode.  If it is low as reported then the associated plate, terminal 22 should be way high because it isn't conducting.  Try rewetting the solder joints at terminals 21 and 22 as well as tube pins B6 and B8.

Looking at the other readings, something is off in the power circuit.



Offline mchurch

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Reply #2 on: April 06, 2012, 05:21:11 AM
I haven't got my instructions handy, but is there any chance the transformer terminals are mislabelled. I seen to recall that in another thread someone had a transformer with the label not agreeing with the terminal numbers cast on the transformer. That is an easy thing to check as it is visual.

Like I said this is just a thought.

Cheers

Mike



Offline TimH

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Reply #3 on: April 06, 2012, 06:52:17 AM
Grainger,

Thanks for the reply.

Oops.  Make that -5VDC at 22 not 21.  Sorry about that.

There is 5.8 VAC from transformer T4 to transformer T5.

mchurch,

Thanks for the info about the terminal numbers.  I did check for the problem, and the labeling is correct.



Offline Grainger49

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Reply #4 on: April 06, 2012, 07:40:42 AM
Mike,

5.8V AC will probably give you 6.3V DC once rectified and filtered.  Try reading from pin 4 to pin 5 on any tube.  That is what matters anyway.

Sounds like you are OK.