Fender OPT Secondary Network

what's up with this weird (weird= i don't understand) network circled in red?

this is a newer Fender DeLuxe "Vintage Modded" amp

osc swamper?  ain't no headphone jack on this amp,  or is there?

thanks!

10 Ohm 18 Watt Zobel resistor?

Looks like they hired some young kid trained in switcher design.

The zobel works above 35KHz.... my gitar don't go that high. It could tame a peak in the OT which might upset the NFB.... but there's hardly-any NFB here on nominal load, and no huge rise at no-load.

Also note the 22pFd in the NFB leg-- a rise at 2.5MHz??

Somebody is getting paid by the part.

this amp has some other problems, every once in a while it will lose all signal and start going into an on again/off again burst of weird noise at about 2 second intervals, it does this even with the PI tube pulled,

this problem is mentioned online,  there are jumpers on the pc board that lay right across the HV traces, heater traces get jumped over the HV traces, the bare metal sits right on the trace, so they left white silk screen paint on the board under the traces as insulation, we removed all the jumpers and raised them off the board, but it still makes the weird noise, so the OPT might be the culprit considering the weird network,

darn, looks like a take-a-part is in order, 

Ive had one or two issues with the switching speaker jacks on modern Fender gear ,I had a switch contact on one of the ouptut jacks go intermittant ,definately well worth a look , it effectively shorted the output terminals ,sound dropped away to almost nothing and the amp sounded like it was osscillating a bit ,very similar to what you describe,

maybe the new resistor network is purely there for safety of the output transformer , in case of misuse or intermittant speaker cableing etc

Yeah I remember now ,the grounding switch contact on the main speaker jack wasnt dissengaging properly when a jack was plugged into it ,it had me headscratching for a bit too .

CJ said:

ain't no headphone jack on this amp,  or is there?

Click to expand...

I don't see one, however I had a newer Marshall head in recently that had a flaky headphone jack.  The  fingers would lose contact and no sound from the speaker out!  Cleaning didn't fix it and the owner never used the phones jack so I soldered the terminals together.

The use of multiple resistors just seems like production cost reduction - if you have those resistors already on the board then you keep the part inventory minimised.