Strange squealing in amp when powered up.

[martin manning]

It's wired as a FWB with 640VAC input = 904V

[ToneMerc]

Look at his HV board, doesn't he have the wrong board for the Twin style PT with the CT. His existing board would be fine if he had used the 026554 non-CT PT...correct?

TM

[martin manning]

That's right. The HV board needs to look like the #124 layout for that PT- FW rectifier. Glad nobody got hurt!

[talbany]

The 290FX is for Twin Dual Showman Bassman 100 etc CE dist has labeled for the replacement https://secure.cedist.com/ Ahh I see it now FWB.. Thanks M


Things I don't like about FWB.

1 Bridges fail more readily because all it takes is for one of the 4 segments to short . If you don't have a bridge, then usually there is a string of 3 or 4 diodes, so you get a few "lives" before your rectifier totally shorts out.
2. PT run hotter!!

Tony

[rogb]

According to the #102 layout posted, the HV CT is grounded, and there is an FWB with the diode anode to ground.

Where#124 has HV CT and FW rec

Is this correct?

[Structo]

He's right, I never noticed that #102 had a bridge.

[ChrisM]

According to the #102 layout posted, the HV CT is grounded, and there is an FWB with the diode anode to ground.

Where#124 has HV CT and FW rec

Is this correct?

No
A FWB won't have a HV CT going to ground.

[talbany]

Yeah !! WOW.. I think I remember what happend.. The 102 Power transformer was a Twin Export.. that transformer used a FWB..Since I only edited the Board I must have forgotten to remove the CT wire.. The actual 102 layout was edited from the 124 so this is the only reason why I can think of as to why I would change the rectifier board.. Good catch and sorry if this caused anyone any pain and surprised as to why we didn't catch this earlier..The CT has been removed from the layout

Tony

[rogb]

According to the #102 layout posted, the HV CT is grounded, and there is an FWB with the diode anode to ground.

Where#124 has HV CT and FW rec

Is this correct?

No
A FWB won't have a HV CT going to ground.

Oh I know this Chris, I really know this as I learned my rectifier stuff the hard way

[martin manning]

Tony, the transformer listed on the layout is 026554. The Hammond replacement for that, 290SX, is 340VAC CT for a FWB. It has a shield lead that should be grounded, but it's gray. The bias supply is a separate winding, brown-brown, so I think there should be a brown lead going to ground from the transformer for that, and the bias lead going to the board should be brown too. The red-yellow CT could be connected to the center of the reservoir stack like the Twin.

[rogb]

Just looked at the Ford Mustang layout and he uses FW with CT to ground. I guess he adapted it to suit his transformer stock.

So the FM is an adaptation not a replica as #102 is?

[talbany]

Tony, the transformer listed on the layout is 026554. The Hammond replacement for that, 290SX, is 340VAC CT for a FWB. It has a shield lead that should be grounded, but it's gray. The bias supply is a separate winding (brown-brown on the Hammond), so I think there should be another lead going to ground from the transformer for that. Don't know what color that would be on the original. Okay, brown from the schematic you just posted above, and the red-yellow CT could be connected to the center of the reservoir stack like the Twin.

M
As you know looking at the schematic he could have easily gone FW. So I went back through my notes on this one and can't find anything on how and why I went to the FWB using the Red Knob Twin P EX-PT It could have been a conversation with perhaps Brandon or another source that I got that info from. I have not actually seen the amp yet but do remember at some point in my research getting some info on 102 and how he had it wired as FWB.Also I thought I had a schematic of the export version w/part numbers in my HD that might be slightly different than the 290 and the schematic but can't seem to find it. If I do perhaps we can shead a bit more light on what exactly how it might have been wired..I'll eed some time to look this over and re-edit as needed..Getting Old is a Bitch!!


All The Best..

Tony

[martin manning]

If that "The Twin" transformer was the one used in the original amp than it was wired as a FWB. The HT voltage would be too low as a FW. Here's the equivalent for Fender 026477, the model number shown on the The Twin schematic and also listed as replacement for Tonemaster. I guess Export or not doesn't really matter, the secondaries are 175-0-175 for the half-power mode. Wired as FW it'd have B+ around 220.

[67plexi]

The Ford#102 ODS used a Fender Tone Master PT Export primary voltage.
14.80 lbs. https://tubeamparchive.com/viewtopic.ph ... 73&start=0

[talbany]

OK The 026554 is as the schematic I posted list output 477 no load FWB. 1/2 power lists 236 FWIW.. The 554 has the multi taps and the 477 does not..Just wanted to verify this

https://tubeamparchive.com/viewtopic.ph ... c&start=15

I'll make the appropriate changes.. Thanks for the Help everyone!!

Tony