Twin Reverb reissue Power trans question.

[lo-watt]

I feel like i know the answer but i just wanted to make sure. I had to get a BF TR Power transformer for a 65 Twin reissue and the only difference was the secondary windings were slightly different. On the reissue,there are no center taps and the is a separate winding for the 55v bias. On the BF trans,there are center taps for the heaters and the HT winding which has a single tap for the bias not a separate winding. These ARE interchangeable right?

[Justin Thomas]

You can just cut & tape off the CTs and use the PT. The bias supply may need a bit of finaigling; since it has an actual winding instead of a tap like the origibal, I believe you would simply ground one end of the winding & use the other end as your bias "feed."

I've heard that the footprints are also different between the RI & Vintage Output Trannies, so the PTs may also be slightly different. But it definitely should be able to be "made to work."

Others will likely have more details or corrections.

Justin

[nickb]

You can just cut & tape off the CTs and use the PT. The bias supply may need a bit of finaigling; since it has an actual winding instead of a tap like the origibal, I believe you would simply ground one end of the winding & use the other end as your bias "feed."

I've heard that the footprints are also different between the RI & Vintage Output Trannies, so the PTs may also be slightly different. But it definitely should be able to be "made to work."

Others will likely have more details or corrections.

Justin

I don't think that is right for the HT as it will give you double the voltage. The BF uses a full wave rectifier while the RI uses a bridge. Therefore you will need to modify the bridge rectifier by lifting or removing the ground connection. There's also a 8200pF cap that either needs to be removed or replaced with a 4700pF 2KV version. See sketch:

[Justin Thomas]

^^^^^^^^ pay more attention to this guy than me! ^^^^^^^^
(In other words, I made mistakes)

Jusrin

[lo-watt]

I don't think that is right for the HT as it will give you double the voltage. The BF uses a full wave rectifier while the RI uses a bridge. Therefore you will need to modify the bridge rectifier by lifting or removing the ground connection. There's also a 8200pF cap that either needs to be removed or replaced with a 4700pF 2KV version. See sketch:

[ATTACH=CONFIG]53901[/ATTACH]

Ok..So i understand the two different rectifiers, So ill leave CP10 disconnected, connect the new 55v to CP9,the center tap of the HT to CP15 while cutting the trace that connect CR1,CR3,and the two HT to CP11,CP12 as in the schematic.

[lo-watt]

Unless either of the CT are disconnected? the HT tap is as follows from top to bottom,HT,55v,CT,HT on the new one. The Mojotone/Heyboer is a direct drop in for the 65 Reissue physically

[nickb]

Unless either of the CT are disconnected? the HT tap is as follows from top to bottom,HT,55v,CT,HT on the new one. The Mojotone/Heyboer is a direct drop in for the 65 Reissue physically

You MUST use the CT of the HT winding.
You MUST NOT use th CT of the 6.3V winding.

There is another wrinkle to to this that I thought of later. The standby switch is in the ground return path. That means that as I drew it the bias supply will be )v when you first turn close the standby switch. The 6L6 will take a big gulp of current for a few 100's of milliseconds until th ebias supply charges and it might be enough to blow the HT fuse.

It would be best to move the standby switch to between the +ve output of the rectifiers and the first filter cap. I add a revised sketch later (when on the right computer).

[lo-watt]

Thank you for the advice,Ill wait on the revised sketch. I gotta order a new thermistor anyway

[nickb]

Revised version. Note you will have break into the connection from the rectifiers to the filter caps in order to wire in the standby switch.



PS: There's a further complication I just spotted. The bridge rectifier is rated at 800V. For a full wave rectifier, as we now have, the diodes need to be at least 2x the peak voltage. I think the easiest thing to do is just forget about the on board bridge and use 4 1N7007, that's two in series for each side of the HT winding with the common cathode going to the standby switch. This will make it much easier to modify. You may not need to even lift the main PCB to do it.

[lo-watt]

So,if im reading correctly,55v bias to CP9,no connection to CP10,Center tap of HT to CP16,HT to CP11 and CP12,connection REMOVED to CP15,CR2 to Standby to CP23/CP21 junction.

[nickb]

So,if im reading correctly,55v bias to CP9,no connection to CP10,Center tap of HT to CP16,HT to CP11 and CP12,connection REMOVED to CP15,CR2 to Standby to CP23/CP21 junction.

That's the idea but see my addition abut the diode rating.

[lo-watt]

Just saw it.

[lo-watt]

Can i just replace CR1-Cr4 with 1N4007? Did you mean 1N4007 not 1N7007? The board is already out.

[Jazz P Bass]

Misprint.
1N4007 diode is what you want.
(1N7007 does not exist)

[nickb]

Misprint.
1N4007 diode is what you want.
(1N7007 does not exist)

Indeed it was a typo - Thanks.