Blues Jr III transformer wiring question

[chikov]

I met a guy today who brought with him from UK a Blues Junior 3 and he asked me if I can help him rewire it to 120V from 230V. I have the manual, that I attached, but it does not really show how to wire it to 120V. I tried wiring for 100V but instead of White wire I connected white/black to the neutral, but I got needed voltages on the Nods only when my Variac was at 112V AC input voltage. Does he need to buy a PT that is made for the US market?
Another strange thing... On the blue wire that goes to the OT (by the diode D11) I should read according to schematics 29.4AC, but I am reading 770V AC... Does anyone know why is there AC in the first place and why is it so high?
Thank you...

[Stevem]

Well when all else fails and since you have a Veriac, do this.
Yank out all the tubes and pump in 6.3 volts into the green heater wires on the PT secondary side, then on the primary side of the PT find the wires / terminals that now have about 120 volts across them.

[martin manning]

I tried wiring for 100V but instead of White wire I connected white/black to the neutral, but I got needed voltages on the Nods only when my Variac was at 112V AC input voltage.

I think if you wire it for 100V, but connect S2B to Black* instead of White you will get what you need.

*Meaning the P9-P10 Black and Black/Green junction.

[pompeiisneaks]

I may be misunderstanding your question, but the schematic shows how the 120V should be wired, adn shows the export wiring in a box below. Unless something is wrong with the transformer, the wiring for 120V is here:

BJIIIWiring.PNG

Basically S2A is the Black Wire
S2B is the White Wire

for 120V operation.

Or am I crazy

~Phil

[martin manning]

Note the different part numbers for domestic and export PT's. The domestic unit appears to have a single 120V primary winding.

[pompeiisneaks]

Oh gotcha, so I am crazy

Didn't see they were separate part numbers. It seems almost like the export model doesn't have a 120V winding then no? Only 100, 220 and 240?

~Phil

[martin manning]

It seems almost like the export model doesn't have a 120V winding then no? Only 100, 220 and 240?

Not as shown, no. Only 100, 230 and 240, but based on those I think the dual primaries are 120 end-to-end.

[pompeiisneaks]

Oh yeah that is quite often the case isn't it. swapping between the two is just parallel or serial for those two windings.

~Phil

[chikov]

When I tried to connect just the coil on top between the violet and black and green wire the voltages Were close to where I needed but it with SAG every time I put a load on it. Just now reconnected black and green Wire with the black and put a neutral wire in it and black and yellow with black and red ( thus connecting both of these windings in parallel) it gave me the proper voltage on the node 1 ( about 324VDC). That sounds good but I encountered something strange.
On the schematic it’s shows that I should have on the output transformer on its primaries 29.4 V AC. Between a ground and the brown wire I get none but between ground in the blue wire I get anywhere between 700 and 2000 VAC ( after the tubes warm up).What is going on there? Does anyone know?

[martin manning]

The 29.4 VAC on the schematic is a signal voltage with the specified 10 mV at the input. The high VAC on the blue side may be an oscillation. I have read that these amps can break into oscillation when they are out of the cabinet. Did you check/replace the two diodes D11 and D12?

[martin manning]

Oh yeah that is quite often the case isn't it. swapping between the two is just parallel or serial for those two windings.

True, provided they are both 120VAC. Export PT's sometimes have creative ways of accommodating multiple line voltages.

[chikov]

I just wanted to tell you all that putting bothof these primery coils in parallel worked. The node voltages are about 8 Volts or so lower but the amps sounds great and the owner was very happy. I wish the instructions would have been more clear but, oh well, that is why we have one another- to help in moments like these. Thank you for all your help