Fender Twin Reverb UL 135watts

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Hi


I have an old Fender Twin Reverb Ultralinear 135watts(1981) amp with a blown output transformer. I have ordered a replacement from Hammond, model No: 1750WR. It is stated that it is a replacement for Fender's 013691 output transformer. This 1750WR transformer has a primary impedance of 2000 CT Ohms. Will this impedance match 4 of 6L6GC tubes. I do not understand how the output impedance of a output transformer is used to match the load impedance of the tubes. I have attached the datasheet for this transformer and 6L6GC tube. Please assist.


Thanks


Carlos
 

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I have an old Fender Twin Reverb Ultralinear 135watts(1981) amp with a blown output transformer. I have ordered a replacement from Hammond, model No: 1750WR. It is stated that it is a replacement for Fender's 013691 output transformer. This 1750WR transformer has a primary impedance of 2000 CT Ohms. Will this impedance match 4 of 6L6GC tubes. I do not understand how the output impedance of a output transformer is used to match the load impedance of the tubes.
Twin Reverb Ultralinear 135W usas 4 6L6 tubes in push pull parallel (2 tubes per side) and expects tp "see" a 2000 ohm plate to plate lload.

The Output transformer does not have impedance by itself but converts speaker impedance to that needed for the tubes.

So IF you connect an 8 ohm speaker to 8 ohm secondary tap (from black to green) or a 4 ohm speaker (from black to grn/yel), you will have 2000 ohms plate to plate (brown toblue).

No need to dig deeper, that´s enough data to repair that amplifier.

Hammond is excellent quality iron so it will work fine.
 
Hi Carlos,
für two pairs of those 6L6-GC's I'd expect half the datasheet's plate-to-plate load value, i.e. 2800 ohms. I guess Fender fell below that value in order to get those 135 watts, i.e. more than 110 watts that had to be expected from the datasheet. Don't forget this happens at the expense of tube lifetime!
Best regards!
 

PRR

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Joined 2003
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...two pairs of those 6L6-GC's I'd expect half the datasheet's plate-to-plate load value...

Many combinations of V and Z will make the same power.

Fender could estimate or experiment his own answers.

The 4k/pair loading seems to come from 6L6 AB2 condition (3,800) where Vg2 is held down to suit original 6L6 spec and Z is dropped to suck the current. The 5881 had higher Vg2 rating and could pull 4k/pair in AB1 for about 40 Watts (Bassman 5F6a). The 6L6GC has even higher rating for P and G2, and you can do 65 Watts per pair in about 4k, and even in UltraLinear.

You can build a marketable radio or amplifier on the datashet suggestions. Building a market-beating amplifier may need a little thought and much smoke-testing.
 
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