I have a Woodside STA35 stereo power amp (using EL-34 power tubes) that has
laid around unused for about 12 yrs. What precautions should I take when
starting it up...eg should I use a variac ...and if so, what's the
recommended procedure with it ? Does it require a speaker load to be
connected ?
Thank you,'
Ray

in article , Ray Thomas at
wrote on 6/2/05 7:38 AM:

I have a Woodside STA35 stereo power amp (using EL-34 power tubes) that has
laid around unused for about 12 yrs. What precautions should I take when
starting it up...eg should I use a variac ...and if so, what's the
recommended procedure with it ? Does it require a speaker load to be
connected ?
Thank you,'
Ray


Ray,

If you have access to a variac, by all means use it. If you don't, you can
wire up the unit in series with a 60W light bulb which will drop the mains
voltage to the amp.

I usually start at about 20V input, and gradually raise it to 120V over the
course of many hours. I monitor the current to see if there are any shorts.
I check the cans for heat to see if they are leaking, and look underneath
for goo. I turn off the lights to be sure that the plates aren't red. (it's
a good idea to replace the coupling caps to the output tubes as a matter of
course).

If your satisfied that there are no gross defects, check your voltages &
etc. after plugging it directly into the mains.

"Ray Thomas" wrote in message
...
I have a Woodside STA35 stereo power amp (using EL-34 power tubes) that
has
laid around unused for about 12 yrs. What precautions should I take when
starting it up...eg should I use a variac ...and if so, what's the
recommended procedure with it ? Does it require a speaker load to be
connected ?
Thank you,'
Ray

Jon has answered your questions fully, except for the question of
the speaker load. You might be wise to put a dummy load, 8 Ohms 10W
across each output. The Woodside amp uses transformers designed by
Arthur Radford. In the technical specification of the STA25, from which
the STA35 is developed, Radford stated that the amplifier can run
indefinitely at full power into either a short circuit or open circuit
load. But why would you want to do that?

Iain

"Ray Thomas" wrote in message
...
I have a Woodside STA35 stereo power amp (using EL-34 power tubes) that
has
laid around unused for about 12 yrs. What precautions should I take when
starting it up...eg should I use a variac ...and if so, what's the
recommended procedure with it ? Does it require a speaker load to be
connected ?

**I assume it uses a solid state bridge rectifier? If so, use your VariacT
to slowly power up the amp, with the tubes removed, whilst monitoring the
Voltages across the first HT capacitor/s. Spend at least 24 hours gradually
powering up. This should ensure proper forming of electrolytic caps.


--
Trevor Wilson
www.rageaudio.com.au

"Trevor Wilson" wrote

**I assume it uses a solid state bridge rectifier? If so, use your
VariacT to slowly power up the amp, with the tubes removed, whilst
monitoring the Voltages across the first HT capacitor/s. Spend at
least 24 hours gradually powering up. This should ensure proper
forming of electrolytic caps.

I would go with the tube pulling too, and the monitoring of a cap,
but which do you mean by the first one? I would follow the one with
the lowest voltage rating, which is the last, usually, from the
point of view of the power supply.

With the valves removed, there will be no current to drop the
voltage at each stage, so caps further down the supply may go over
their voltage limits. Perhaps if this would be the case, valves can
be added to each stage in progression as the voltage is brought up
to full level.

But there isn't an ideal way of reforming multiple caps in circuit.
Really you need to monitor the leakage current, and back off and
wait whenever it gets jittery or too high. The time can be long or
short. So better to err on the long side: your suggestion of 24 hrs
seems reasonable.

cheers, Ian

"Ian Iveson" wrote in message
o.uk...
"Trevor Wilson" wrote

**I assume it uses a solid state bridge rectifier? If so, use your
VariacT to slowly power up the amp, with the tubes removed, whilst
monitoring the Voltages across the first HT capacitor/s. Spend at least
24 hours gradually powering up. This should ensure proper forming of
electrolytic caps.

I would go with the tube pulling too, and the monitoring of a cap, but
which do you mean by the first one? I would follow the one with the lowest
voltage rating, which is the last, usually, from the point of view of the
power supply.

With the valves removed, there will be no current to drop the voltage at
each stage, so caps further down the supply may go over their voltage
limits. Perhaps if this would be the case, valves can be added to each
stage in progression as the voltage is brought up to full level.

But there isn't an ideal way of reforming multiple caps in circuit. Really
you need to monitor the leakage current, and back off and wait whenever it
gets jittery or too high. The time can be long or short. So better to err
on the long side: your suggestion of 24 hrs seems reasonable.

**Agreed. Monitoring ALL caps would be sensible.


--
Trevor Wilson
www.rageaudio.com.au

But there isn't an ideal way of reforming multiple caps in circuit.
Really you need to monitor the leakage current, and back off and wait
whenever it gets jittery or too high. The time can be long or short. So
better to err on the long side: your suggestion of 24 hrs seems
reasonable.

**Agreed. Monitoring ALL caps would be sensible.


actually, the most sensible course of action is to REPLACE ALL electrolytic
caps on this 40+ year old amp BEFORE ever powering it up.

yeah, it might work with the old caps, for a while, but why chance the
irreplaceable trannies and the expensive GZ34 rectifier it likely has? You
also risk the expensive EL34 tubes, if they are NOS, you could by a 100's of
caps for what those are worth!

electrolytic caps should be replaced in old equipment BEFORE they take out
hard to find parts!