voltage PT #183

[grtamp]

I have a trafo with 350-0-350 ,can be fine for a #183 amp? It's high voltage?

[heisthl]

easy rule of thumb is add together and multiply by .7 so 350 + 350 = 700, 700 X .7 = 490volts. Real world it will probably be a little lower.

[grtamp]

Thanks heisthl , I'll use it for another amp.

[CHIP]

I think that Tranny would work for a #183. Do you think it's too low? High?
It will need at least 6.3V @ 7a for the filaments.

[grtamp]

Maybe 350V it's too high....
Heater wiring 3.15-0-3.15V 7.5A , measured 6.6V
Bias wiring 57V

[67plexi]

350-0-350 is fine for #183.

just use a 6k 10 watt resistor on the filter board to drop B+2.

My last #183 build used a 350-0-350


Steve.

[pazzo63]

Ciao the REAL question is what are the specs of tf 130 power transformer used on DUMBLE ODS ??you should get 465 volts on the plates , i think a 360-0-360 power trafo would be fine , with loaded circuit 345-0-345 CIAO

[mdroberts1243]

Ciao the REAL question is what are the specs of tf 130 power transformer used on DUMBLE ODS ??you should get 465 volts on the plates , i think a 360-0-360 power trafo would be fine , with loaded circuit 345-0-345 CIAO

This talk of TF130 and 465VDC (as per the talbany layout) is confusing me... On supplier sites the TF130 crosses to Fender part numbers 125P34A and 022756 which seem to lead to transformers that produce about 420VDC from the 320-0-320 secondary (Fender Twin/Showman levels)... where does the 465V come from?

I haven't found a link between TF130 and 465V... I'm wondering if the original transformers were designed for typical Fender levels at 115VAC or 117VAC instead of today's 120VAC... but the math doesn't even work in that case.

[martin manning]

FWIW, the Fender Twin Reverb AB763 schematic (1964) shows PT 125P34A and 360V on the 6L6 plates; 340 VAC at the HT.

(Edit: 460V, not 360... typo)

[mdroberts1243]

FWIW, the Fender Twin Reverb AB763 schematic (1964) shows PT 125P34A and 360V on the 6L6 plates; 340 VAC at the HT.

I found this bit of history on an amp rental site: "The rating of the amplifier's output power was also upgraded to 100 watts. Fender factory schematics show slightly higher voltage on the output tube plates when compared to the older AB763 circuit. Some say that this accounts for the higher output power. It should be noted however, that the power transformer part number for the AB763 and the later circuit designs are identical, being part number 022756 (125P34A), and the specification of that part number did not change. The transformer output is rated at 640vCT at 450ma when its primary receives a 117v input. Other parts of the power supply are essentially the same, so some mystery surrounds the increase in power. One possible answer is voltage delivered to the amplifier from the wall plug. In North America, wall outlet power is considered to be 117v nominal, plus or minus 10 percent. Fender may have originally rated the amplifiers when plugged into the voltage available at their factory, which may have been as low as 105v. Maximum operating voltage would be about 127v. Quite possibly CBS saw fit to rate the amplifiers power at maximum input voltage, thus gaining an "upgrade" with no change, and at no cost whatsoever."

Most of the 125P34A replacements quote 640VCT at 450mA (320 per side) at 120VAC, but a few websites quote the Hammond as delivering 335-0-335 (it doesn't, and the label in their pictures shows it spec'ing at 320).

I think I'm going ahead with a Hammond PT, and hope the 40V lower B+ will lend a bit of bluesy tone due to lower head room.

[talbany]

1963-1967. During this time the BF Twin AB763 output was rated at 85 watts into a 4-ohm speaker load...
Note..Back then they rated power on the conservative side

FWIW, the Fender Twin Reverb AB763 schematic (1964) shows PT 125P34A and 360V on the 6L6 plates; 340 VAC at the HT.

Martin shouldn't that be 460v.

Tony

[pazzo63]

Ciao , early silver face fender AA768 had bigger transformer ,100w not 85w and the voltage was higher, i think the power transformer was laydown like tf 130 ,i think 465v is correct , probably older Dumbles had lower voltage ( more fenderish)Anyway i prefer 465v for dynamics BEST

[talbany]

Ciao , early silver face fender AA768 had bigger transformer ,100w not 85w and the voltage was higher, i think the power transformer was laydown like tf 130 ,i think 465v is correct , probably older Dumbles had lower voltage ( more fenderish)Anyway i prefer 465v for dynamics BEST

Pazzo
AA768 Silverface Showman PT pretty much the same as a Twin..Showman's ran 10v higher (470v) on plates than the Twin's BUT..Twin has more preamp tubes!!

Fenders Specs..

Model/Circuit Number: AB763, AC568, AA768
Years of Production: 1968 - 1970
Era: Silverface
Configuration: Piggyback
Controls: Silver forward facing w/ blue labels
Knobs: Black skirted w/ chrome center, numbered 1 - 10
Faceplate
Front: Normal: In, In, Bright Sw, Vol, Treb, Bass - Vibrato: In, In, Bright Sw, Vol, Treb, Mid, Bass, Speed, Intensity - Pilot Lamp
Rear:
Cabinet
Dimensions: Head: 8¼ x 23¾ x 9½, Dual Showman: 45½ x 30 x 11½
Hardware: Knurled Studs
Handle: 3 Black Strap Handles
Feet: Glides
Corners: Chrome Corners with Lip
Covering Material
Tolex/Tweed: Black Tolex
Grill Cloth: Blue Sparkle Grill Cloth with Aluminum Frame
Logo: Grill mounted, raised, chrome & black, script
Weight:


Speaker
Size: Showman 15 Head: 1 x 15
Impedance: Head: 8 ohms ; Cabinet: 4 ohms
Model: JBL D-130F
Effects: Tremolo
~Watts: 85 watts


Tubes
Pre amp: 2 x 7025
Power: 4 x 6L6GC
Bias: Fixed Bias
Rectifier: Solid State
Comments: The Showman 15 and Dual Showman cabs were discontinued at the end of `68 but the head was available until `70.

Avg Monthly Price
Month Qty Avg Price
2007-08 4 574
2007-10 2 488
2008-02 1 700
2008-05 1 542
2008-09 2 561
2008-12 1 575
(ALL Months) 11 564

Year Qty Avg Price
1967 1 650
1968 8 545
1969 1 500
1973 1 700
(ALL Years) 11 564

This talk of TF130 and 465VDC (as per the talbany layout) is confusing me... On supplier sites the TF130 crosses to Fender part numbers 125P34A and 022756 which seem to lead to transformers that produce about 420VDC from the 320-0-320 secondary (Fender Twin/Showman levels)... where does the 465V come from?

BTW...125P34A PT on Dual Showman... Plate voltage loaded 470V..Once again 10v higher than the Twin... If the 5-10v difference bothers you wait till you plug into a club with 75 year old wiring and running off the same circuit as the ice machine, microwave and god knows what else..


Tony

[pazzo63]

Cao Tony i was meaning the AA 768 there is a schematic on Dave Funk Tube amp workbook pag 402 360-0-360 power transformer, like a super reverb but 4 6l6 tubes ..

[martin manning]

Martin shouldn't that be 460v.

Yes, didn't proof read well enough; thanks for pointing it out.

Mark, The Hammond 290FX Twin PT replacement puts out 423V from 122VAC at the wall in my ODS. It was ~440V unloaded, as I recall. It is supposed to produce period correct voltages, I believe. Lots of successful builds have been done using this unit, and it sounds great to my ears. I see there is now a 291FX, same ratings, but with M6 steel lam's.

I have no doubt that a marketing type would quote power at peak line voltage, especially at a time when power ratings were going up. I wonder if the original literature supplied with the amps specified a line voltage along with the rated power?