Ampmaker WF-55 squeal

[Steve Blackdog]

Hello all.

I have finished my Ampmaker WF-55 amp build and have been testing before plugging anything in.

I am getting a high pitched whistle through the speaker. The volume pot does not change the volume of the squeal, although there may be a slight change in pitch.

It is way too loud to ignore.

If I waggle the GT 12AX7R (Sovtek 12AX7WC) pre-amp tube the squeal changes, but does not disappear. It starts once the tubes have had 30 seconds to warm up a bit. If you tap the tube with a pencil, there is no change.

I assume I have dud pre-amp tube. However, as I am in testing mode, could it be something else?

I will get myself a spare 12AX7, but I would appreciate any alternative theories.

Cheers

Steve

[Helmholtz]

Schematic?

[nickb]

http://www.ampmaker.com/images/ak00kit/ak00sc2.jpg

http://www.ampmaker.com/wf-55-constr...ual-842-0.html

I assume you have meticulously checked every wire and component? If so, then pull V1 and see if that helps. If it does that put it back and connect V1 pin 7 to ground with a short wire. What happens?

[g1]

It's supposed to be basically a 5F1 Champ, so first thing I would try is disconnecting the feedback wire from the speaker jack.
edit: looks like feedback wire goes to 4 ohm tap rather than speaker jack.

[Steve Blackdog]

http://www.ampmaker.com/images/ak00kit/ak00sc2.jpg

http://www.ampmaker.com/wf-55-constr...ual-842-0.html

I assume you have meticulously check every wire and component? If so, then pull V1 and see if that helps. If it does that put it back and connect V1 pin 7 to ground with a short wire. What happens?

If you pull v1 squeal free.

[Helmholtz]

^^That, and if this stops the noise reverse PT primary wires.

Edit: Typo, meant OT not PT!

[Steve Blackdog]

http://www.ampmaker.com/images/ak00kit/ak00sc2.jpg

http://www.ampmaker.com/wf-55-constr...ual-842-0.html

I assume you have meticulously check every wire and component? If so, then pull V1 and see if that helps. If it does that put it back and connect V1 pin 7 to ground with a short wire. What happens?

V1 pin 7 goes to pin 2 of the vol pot. Do you mean disconnecting if from the pot, or adding the short ground wire and leave the connection to lug 2 on the pot?

Thanks for help.

Steve

[Steve Blackdog]

^^That, and if this stops the noise reverse PT primary wires.

What will that do?

[Helmholtz]

What will that do?

I might change undesirable positive feedback to correct negative feedback by phase reversal.

[Steve Blackdog]

I might change undesirable positive feedback to correct negative feedback by phase reversal.

I see, thanks!

I have heard of people swapping the wire around on the OT.

[Steve Blackdog]

http://www.ampmaker.com/images/ak00kit/ak00sc2.jpg

http://www.ampmaker.com/wf-55-constr...ual-842-0.html

I assume you have meticulously checked every wire and component? If so, then pull V1 and see if that helps. If it does that put it back and connect V1 pin 7 to ground with a short wire. What happens?

Hi Nick,

I added a short wire to v1 pin 7. Made no difference. Tomorrow I will try swapping the wires from the PT.

[pdf64]

Yes, swap the wires to the primary of the output transformer (OT).
O is next to P, it was a typo.

[nickb]

Hi Nick,

I added a short wire to v1 pin 7. Made no difference. Tomorrow I will try swapping the wires from the PT.

Ok Great. The ojective was to eliminate wiring errors and/or pickup in the wire to pin 7. Onward and upward!

[Helmholtz]

I have heard of people swapping the wire around on the OT.

Sorry, PT was a typo. Of course I meant the OT and my explanation refers to this. Swapping PT wires would have no effect.

(Excuses: weak eyes, foreign language/abbreviation, late at night e un po di vino rosso.)

[Steve Blackdog]

Yes, swap the wires to the primary of the output transformer (OT).
O is next to P, it was a typo.

BINGO!!!

I swapped the OT primary wires and the squeal has disappeared. Plugged in the guitar. Really really pleased with it!

Thanks for your help folks.

Cheers

Steve