SE5a power transformer help?

[Pryde]

Hello Folks,

Need some assist on this little 5 watt amp: Ampmaker SE5a. Just built it up for myself (kit amp) and started first power up and taking voltages.

With no tubes in and standby on: The PT heaters are only producing 3.4v AC when measured across the windings (should be ~6.5v). Checked the 100 ohm resistors (R11 and R12) and they are in spec.

I am getting 118v AC at the on/off switch (S1) so I know wall power is ok.

Also measured the primary and am getting 198v AC where it meets D1/D2 rectifier diodes (should be getting ~400v per instructions)

Does this mean the PT is faulty?

schematic attached

[Enzo]

Please note from your schematic that it shows the amp wired for 240v mains operation. If you wired your power transformer primary as the schematic, that explains why all your voltages are half what they ought to be.

Note the drawing - the primary is two sections wired in series. For 120v operation, those two sections need to be wired in parallel. Thge main fuse probably then wants to be 1A.

[Pryde]

Actually the PT that was supplied is 0-120v on the primary, HV secondary is 190-0-190v, heater is 0-6.3v

The company is UK but the transformer supplied is correct I believe....but open to education if not.

Here is a photo of the primary wiring. It has 2 120v winding pairs with a jumper in the middle (short red wire connecting. Is that making it a 240v PT with the jumper?

[The Dude]

Actually the PT that was supplied is 0-120v on the primary, HV secondary is 190-0-190v, heater is 0-6.3v

The company is UK but the transformer supplied is correct I believe....but open to education if not.

Here is a photo of the primary wiring. It has 2 120v winding pairs with a jumper in the middle (short red wire connecting. Is that making it a 240v PT with the jumper?

Yes, it looks like you have the windings wired in series for 240V, rather than paralleled for 120V operation. (as Enzo already stated)

[Dave H]

...Here is a photo of the primary wiring. It has 2 120v winding pairs with a jumper in the middle (short red wire connecting. Is that making it a 240v PT with the jumper?

It's wired for 240V. The two 120V windings are in series. They should be in parallel as Enzo said for 120V.

[Pryde]

Gotcha. making more sense

For parallel then do I bring those bottom wires (grey/red) up to the 0v on the first primary winding?

Do I then need a short jumper from 0-120v on that bottom set of windings?

[Dave H]

Too slow again! I hate that

Remove the middle jumper then connect a jumper between the two 0V terminals and a second jumper between the two 120V terminals

[The Dude]

NO. You tie the two "0's" together and the two "120's" together to parallel the windings. No different than paralleling a pair of speakers.

Edit: Dave, you got me back!

[Pryde]

Ah. A "duh" moment never to happen again

Corrected it to parallel wiring and what do you know, perfect voltages!

Thank you everyone for the quick and successful help!