Paramour PT2 upgrade wiring question

[DavidS]

Hi

Elaine sent me a pair of new PT2s to replace an original Hammond H300668s in Paramours in which one seems to have shorted out. When I removed the Hammond I thought the PT2 would drop in with the same wiring pattern:

the Hammond had violet/orange/yellow/yellow on one side, and
green/white/black/green/green on the other.

However, the tabs on the PT2 are labeled as follows:
(1) OV (2) 300V (4) 0V (5) 120V (no tab 3) and on the other
(6) 0V (7) 2.5 V (8) 0V (9) GND (10) 6.3 V

The paired yellow leads from the Hammond I think should be at terminals 7 and 8 for the 2.5 V since they are described in the instructions and on the Hammond as for a 2.5V secondary, not tabs 4 and 5 which are 120V; instead the white and black leads which were from the primary should be connected to tabs 4 and 5?

Seems obvious reading the labeling on the PT2, but just wanted to make sure! If my description is unclear I can send a photo of the labeling on the PT2, and the old label on the Hammond.......

Thanks
David

 

[Paul Joppa]

The PT-2 is not an exact replacement; specifically the high voltage winding requires a full-wave bridge, rather than the full-wave center-tap arrangement of the Paramour I.

When we did the Paramour II, we moved the whole HV power supply to sit over the power transformer, but really you just need to wire in four rectifiers in place of the original two, on each channel. I'm sorry if that was not made clear at first. I don't think we have documented this change but it should be relatively easy to do so. You'll need eight replacement UF4007 rectifiers, and I would think two of the terminal strips that fit on the transformer plus a few inches of wire. Call Eileen in the morning and reference this post; I'll ping the headquarters about documentation - probably a couple good pictures will be enough.

 

[DavidS]

Paul, thanks.

Good news is Elaine sent me the transistors and rectifiers. Bad news is I have no idea what to do with them. I'll try to give her a ring tomorrow.

David

 

[Natural Sound]

Pssst... It's Eileen not Elaine.

.

 

[Paul Joppa]

I talked to Doc B and PB, and looked more carefully at the Paramour I that I have - it's had parts scavenged but the power supply is still intact. I think I can write instructions for the conversion, and I believe that  you  can use the wires from the original transformer if you cut them off right at the transformer so they are as long as possible. That should save a lot of re-wiring grief!

It may take me a day or two - I'll post again when I have something. While waiting, you can cut the wires and exchange the transformers. Be sure to mount the new transformer with the "missing tooth (terminal 3) towards the back of the amplifier. Strip the ends of the wires 1/4 inch.

More to come.

 

[Paul Joppa]

First draft, ask if something seems wrong, it probably is:

Replacing the Hammond power transformer with the PT-2
=====================================================

First, cut the wires from the old power transformer RIGHT AT THE TRANSFORMER - so they are as long as possible. Strip the ends of these wires 1/4 inch.

Now here is the worst part - remove the orange wire from the braid in which it is embedded, and unsolder it from amplifier terminal 4. You'll want to move the brown and purple wires away from that terminal so you can get at it without melting their insulation, and there are a lot of other things soldered to that terminal. Worse yet, you must eventually attach two new wires there - that's why you are removing the orange one, to make it a little more accessible. I'm sorry, I apologize, if I coule think of a better way I would suggest it - but I can't.

Then you can exchange the transformers.Be sure to mount the new transformer with the "missing tooth" (terminal 3) towards the back of the amplifier. Don't forget the core ground wire on the back right mounting bolt. The PT-2 terminals should be labelled 1-2-3-4-5 left to right along the back side, and 6-7-8-9-10 left to right along the front. Terminal 3 is missing.

Now you can solder the 2.5v winding, transformer terminals 6 and 7, to the yellow wires that go to the 2A3 socket.

Solder one end of the now loose orange wire to transformer terminal 9, the 6.3v winding center tap. Solder the other end to the transformer core ground lug on the mounting bolt, nearest transformer terminal 5. Now you can solder the green wires to transformer terminals 8 and 10, providing 6.3vAC to the driver tube.

Now the second worst part - adding two new UF4007 rectifier diodes. First, notice that there are already two diodes, from T1 to T5 and from T2 to T5. They have a white stripe at one end, and orientation is important. Both of them have the white stripe at the end that goes to T5. Now you must attach and solder the NON-STRIPED end of two NEW diodes to T4 - that messy terminal with the ground buss, the capacitor negative terminal, and the bleeder resistor. You can put them on the visible side of the terminal strip - cold comfort, but better than none. Take your time, be patient and careful. You have my permission to mutter foul oaths during the process. A strong light and good reading glasses may help. The ground buss wire was always a pain to solder on these amps, so be sure you have good connections.

Once the diodes are  in place, solder the other ends to T1 and T2 respectively. This completes the 4-diode fullwave bridge rectifier. Now you can solder the brown and purple wires to transformer terminals 1 and 2, the 300vAC high voltage winding.

Finally, the black and white 120v power from the power cord is soldered to the 120v winding, transformer terminals 4 and 5.

The usual voltage and resistance checks should be the same as before, except for terminals 1 and 2.

If there are difficulties in this process, post on the Bottlehead forum and we'll deal with them, and revise these instructions if you find a better way.

 

[DavidS]

Paul, thanks to you and the great Bottlehead support squad! Your detailed instructions along with the Paramour II manual pics from Eileen should make this possible. I won't have a free weekend for a few to work on them, but I will send a note along if and when I am operational. I can't wait to hear them alive again.

 

[2wo]

Just a thought, I don't know how complicated your T4 term is but an option would be instead of trying to unsolder the orange wire, clip it, leaving say 3/8-1/2" attached. Remove the insulation and use the wire stub as a terminal extension, so to speak...John