Pilot 402 amplifier. info?

[Hull Rust]

Here's what the email said:

I brought it up on a
variac and all voltages checked out and it passed a signal through both channels
so I thought everything would be good for a rebuild.

I went ahead and totally rebuilt the power supply. Then I ran it and it hums a
lot. Put a scope across the supply and found that it was the source of the hum.

It turns out that the HV winding on the power transformer is only half present.
This is tricky because it shows the correct voltages but the noise on the supply
is only 60hz when it should be fully rectified 120hz. I can explain this more
when you get here.

The tech is a pro who has helped me out on several projects, including a couple of Pilots. I trust him 100%, great guy to work with. He felt bad, said he should have caught the issue earlier in the process.

I just can't afford to put more into it. I wanted to keep going with the 402, but there's a point where it doesn't make sense.

 

[mech986]

Well, check what power transformer raw specs ought to be and put in a Barter Town want ad, someone in tubes forum or other DIY might have something suitable as a decent replacement.

Shame.

 

[Hull Rust]

I'm not a tech so I don't know how to check the raw specs. The part number on the schematic is 55-77.

It came from a Pilot Soloist console. Sold for $560.00 to $602.00 in 1960.

 

[Tom_r]

If you can post the schematic someone may be able to help you figure out what transformer specs you should be looking for. 55-77 is Pilot's proprietary number for that transformer, so is just an internal part number.

One has to wonder where all their internal master parts lists went to spec out their transformers ... probably thrown into the trash during an ownership change: Who the heck would be interested in this old tube crap now that we have transistors! LOL.

 

[Hull Rust]

Here is the schematic.

I will be sending this and other Pilot information to the AK Database next week.

 

[mibag6]

Is there another sheet for the schematic? I don't see the PS on the 2 sheets you have posted. Also, did the tech give a definite description of the failure mode of the winding such as open winding, shorted winding?

 

[Hull Rust]

There is another sheet, I'll get that posted. Shows you what I know, I thought it was for the tuner section only.

The tech had me write this down for future reference:

"One leg of high voltage winding is open and lead is flying / loose. Pin 4 of Rectifier."

He said there was a break in the winding.

 

[Hull Rust]

Here is the other page

 

[mibag6]

Pilot was pretty good about labeling resistance values of windings on their schematics so one can often check the windings out before powering up. Also, sometimes with a digital meter you will get spurious readings of phantom voltages which can be quite aggravating which is what I'm assuming happened here. Some folks will use an analog meter if there is a questionable reading with a dvm but one can see that your tech may have thought all was well when voltages check out ok.
I see they didn't give R values on this particular trans.

 

[Hull Rust]

He's really good, great guy to work with. Just one of those things, it seemed ok at first, but wasn't.

Unless I can find an identical Pilot part, which I know is pretty much not going to happen, I have to walk away from this 402, which is too bad. Doing the mods to mount a new power transformer pushes beyond my budget.

 

[mibag6]

Put an ad on BT. There's a bunch of folks here with stashes of trannies, you might just get lucky.

 

[Hull Rust]

You're right, worth a shot. Thanks for you help, much appreciated

 

[Tom_r]

deleted

 

[Leland47]

Sounds like its raining Pilot 402s.

I love Pilot gear....have 4 of their amps.

I'll keep an eye out for a 402 power transformer....

Edited. LOL...I see Tom_r has 5 Pilot amps...and a 210 preamp....nice.

 

[SixCats!]

Hi all,

Arrrrrrr! I'm in the same boat. That is to say, I too own a PILOT 402 Receiver (pulled from a Console) and (if memory serves) it has a bad Transformers as well.
I'm not sure what I'm going to do with this unit. It's been "shelved" for several years.

SixCats!

 

[mech986]

Hey six, good to see you again!

Guys, is there a Sam's photo facts on this unit? They generally listed troubleshooting values and voltages, and sometimes gave some optional replacement part units (Stancor, Chicago, or Thoradson transformers for example), might be worth a shot to check.

 

[mech986]

Another more expensive option is to contact a transformer rewinder (Heyboer? Or similar) who could do something.

 

[mech986]

https://www.samswebsite.com/en/photofact/details/index/id/119038

Sam's photofact 719-7

 

[mech986]

https://beta.m.box.com/shared_item/https://app.box.com/s/74ouxvcez0fakcw7wr3n

Nope, model 402 console but not the 402 receiver. Not with the 6BQ5 outputs.

 

[Tom_r]

Sounds like its raining Pilot 402s.

I love Pilot gear....have 4 of their amps.

I'll keep an eye out for a 402 power transformer....

Edited. LOL...I see Tom_r has 5 Pilot amps...and a 210 preamp....nice.

LOL, actually 6 amps!

2 x AA-410a 6L6 monoblocks
2 x AA-901 KT66 monoblocks - bought 6 months apart from New England and Midwest but may have been made the same day as one has a serial number four numbers higher them the other!
1 x 232
1 x 260

The PA-911 isn't an amp, it is the first preamp Pilot made and I think it's somewhat rare. It was sold to be used with and powered from the AA-901 amp. However, shortly after the PA-911 was released it was revised to the PA-912 which has it's own power supply.

Now back to our regular programming - sorry for the hijack.