Author Topic: Sunn 2000S power transformer specs?  (Read 4611 times)

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Offline groovaholic

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Sunn 2000S power transformer specs?
« on: August 24, 2002, 01:43:00 am »
I just picked up a 2000S, but it doesn't have a power transformer.  I'm looking at new Hammond replacements, but I'm not expert enough to know which one would be suitable (I will have my tech do the install)

Can anyone tell me the voltage, amperage, etc that I should be looking for?

Thanks!
John Jungblut

Offline JoeArthur

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Sunn 2000S power transformer specs?
« Reply #1 on: August 24, 2002, 01:46:00 pm »
I don't know the exact specs, but your tech should be able to figure out something close from the schematic.

Assuming you are going to keep the dual tube rectifiers, then your transformer will need a 5 volt winding.  Look up the heater current for a GZ34 rectifier, multiply it by two, and that would be the minimum current rating for the 5 volt winding.

The 6.3 volt winding has to supply 4-6650s, one 12AX7 and one 6AN8.  Look up their heater currents, multiply the 6650 value by 4 and add them all together.  That would be the minimum current rating for the 6.3 volt winding.

The power supply shows 510 Volts at the first filter capacitor, which is good as it makes the B+ voltage rating somewhat easy to determine.  The 510 volts would be a peak-voltage (due to the action of the first filter cap), so you would want to determine the RMS value for the input to the cap voltage.  Divide the peak voltage of 510 by 1.414, and you get 360 plus a fraction.  So, your B+ winding would have to be at least 360-0-360, but considering there will be some voltage drop across the tube rectifiers, you will want to go higher to compensate.  How much higher?  Hmm... typically around 40 volts is usually dropped across a tube rectifier, but since the 2000s has two, that would be about 20 volts.  I would be happy with 370 to 375.

As for B+ winding current... well, that's when I would get out the old transformer catalog, match up the above to find something close and then pick the one with the highest current rating... making sure I have more than enough current for the two heater windings.

Then I would worry if it would fit in the stock position!!

Offline groovaholic

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Sunn 2000S power transformer specs?
« Reply #2 on: August 25, 2002, 05:03:00 am »

Offline groovaholic

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Sunn 2000S power transformer specs?
« Reply #3 on: August 25, 2002, 05:29:00 am »
JoeArthur - dude you rock!  That's EXACTLY the explanation I was hoping for.  So, I went to Triode Electronics and pulled up the tube data pages and then I went to Hammond's website and pulled up their transformer descriptions, so I think I'm equipped to make an educated decision now.

One other thing - if I went with diodes instead of 5AR4/GZ34 then I'd only have to worry about 1 set of heater voltage/amperage requirements and it would also reduce or eliminate any drop on the B+, right?  The problem I'm running into is that the 6550's need 6.4A (1.6A each x 4) and none of Hammond's transformers have more than 6 Amps on the 6.3 V filament - would running SS rectification help with that?

Thanks,
 John

Offline JoeArthur

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Sunn 2000S power transformer specs?
« Reply #4 on: August 25, 2002, 07:39:00 am »
Nope... sorry groovaholic.  Each secondary winding on the transformer is independent.  Current required by one cannot be provided by another.

You could use a separate transformer with a single 6.3 volt winding to supply say... just the 4 6550's, assuming you could find one with a 7A rating (safety factor is always good)... and could find a place to fit it in, like maybe under the chassis.

Using solid state diodes instead of the GZ34's will raise the B+ voltage, due to less (much less) being dropped across the diodes.  If you will never use the tubes, then the SS diodes can be wired directly across the tube terminals (cathode to cathode, anode to plate)... and I would probably put a blob of silicone rubber in the tube sockets.  If you do this, then I would stick with a max of 360 or 365 for the B+ winding.  

You might want to consider replacing the first couple of power supply filter caps with the same value but with a 600 volt rating, or series wire two 350 volt or so units of double the MFD value, each  bridged in parallel with something like 220K resistors as most Fender amps do.  Overvoltage on electrolytics ain't a good thing to do.

Offline markgriffiths

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Sunn 2000S power transformer specs?
« Reply #5 on: May 04, 2003, 12:41:48 pm »
Hi groovaholic
Followed your exchange with JoeAArthur and would love to know if you finished the job.
I'm in France and need to wind a 220-40 volt transfo.
Any help from your experience welcome.
Here's my posting :
I have an ex-Hendrix Experience 2000s bass amp used by Noel Redding. Converted in 1968 to 220 volt mains trans. Mains transfo's dead and gone so need data for winding voltages and amperage to have a new 220 volt transfo made. Maybe someone knows how to do the job with solid rectifiers to replace the GZ34s. Any help/suggestions welcome.
My Email : mark.griffiths@wanadoo.fr
Thanks a lot :lol:
Ex-Hendrix Experience 2000s bass amp used by Noel Redding. Converted in 1968 with a 220 volt mains trans. Transfo's dead and gone need data for winding voltages and amps to have a new 220 volt transfo made.