[PhilcoMike]

Ron,

If you want to add USPS insult to injury watch for ground shipment transfer tricks by the boys in brown at UPS. Seems like they will use "last mile" delivery by dropping off a pallet at local post office and let them delivery it. The problem is they don't tell the customer. I am not the only person who gets their mail at a PO Box only for security. No mailbox at home, no delivery by USPS as the stealth package service. Not even a pick it up at the post office notice.

Guess who gets to chase the package back across country and most of the time pay to have it shipped back again?

The only way around this I have found, and this doesn't work all the time, is to only use my PO Box address for the shipment field and add in comments that ground shipments do not allow USPS for final delivery due to no mailbox at residence.

I now return you back to your vintage vinyl FM hour courtesy of Fisher receivers.... :>))

Thanks,

Mike

[Ron Ramirez]

FedEx and USPS have a partnership, also. They call it "FedEx Smart Post."

It's now four days since my transistors were processed through the PO in South Bend, IN, and still no further updates since 03/31. I think the package is probably lost...but I'll give it until the middle of next week before I start trying to get a refund.

Anyone know how to cross reference transistors other than using the NTE cross reference? In other words, is there any way to cross an old transistor to a 2N or 2Sx number? I ask in case I have to buy more TR1009 replacements.

[Mondial]

There are a lot of generic output transistors you can use to replace the originals. Are they the usual TO-3 metal NPN's?

If the supply voltage is less than 60 V, then 2N3055 comes to mind. It was a common output in the 60's and 70's and they are cheap and easily available.

I would not get the NTE replacements. They just rebrand common generic transistors and inflate the price.

If you give me a little more info I can probably suggest an available replacement. I designed consumer high end audio amps in the 80's and 90's. and have some experience in specifying outputs.

[Ron Ramirez]

No, I won't buy NTEs either. I've just been using their replacement guide and then looking for NOS Sylvania/Philips ECG equivalents.

TR1009 is indeed a TO-3 metal can, NPN silicon.

Later today, Mondial, I will post the supply voltage of the 700-T for the output circuit and other pertinent info. I appreciate the help.

[Mondial]

Ron, I found the schematic of the 700-T and looks like the output stage supply rail is + 65V. That's a bit high for the 2N3055, but ON semiconductor makes a higher voltage version as the MJ15015G. Its rated for a Vce of 120V which leaves plenty of safety margin.

http://www.onsemi.com/pub_link/Collateral/2N3055A-D.PDF

Its a versatile NPN silicon output, and can replace any similar style transistor in a vintage receiver or amp. There is also a matching PNP complement available.

Mouser has them in stock at $2.85 in single unit quantity, or $2.30 in lots of 10. If you are considering doing more amp repairs, you might consider getting a bunch of these to have on hand.

[Ron Ramirez]

Well, Mondial, you beat me to it. But I'll go ahead and post the partial schematic of one of the output channels anyway, for the edification of anyone else interested.

[Image: http://www.philcoradio.com/images/phorum...output.jpg]

$2.85 each, eh? Well, that is less than I paid for each of the ECG162s that are, most likely, lost in the mail.

What do you suggest for a wattage value for the two 0.82 ohm resistors, R37 and R39? I still need to order these, so it's just as well that I get resistors and new transistors from Mouser at the same time.

[Mondial]

What I would suggest is 3 Watt flameproof metal oxide films.

These have the advantage of acting as a fuse if the output transistors short, opening and preventing any further damage to the power supply.

What type of resistor were originally installed?

[Ron Ramirez]

I have no idea - the resistance is given but not the wattage. They are light green. I can provide a photo if that will help.

[Mondial]

They might have been small wirewounds. They typically don't open in an overload situation, causing overheating and further damage.

I have seen similar resistors glow like a heating element when overloaded.

If you can, post a photo just to confirm...

[Ron Ramirez]

I'll post a photo later this evening. I can tell you that although they smoked for a few seconds before I cut the power, they did not burn out - they still measure at 0.8 - 0.9 ohm; the two in the right channel (which did not smoke) measure the same. So perhaps the originals are wirewound?

I like the idea of using metal oxide film which would act as a fuse in case of a short. The 63 volt supply to both channels have individual (left and right) fuses. But the metal oxide resistors would be extra insurance.

[Mondial]

Yes they sound like wirewounds. It is probably lucky that you shut the power and they did not open, because if they did, the driver transistors would be blown also.

Its a bit of a tradeoff. The metal films will open but in doing so will blow the drivers and possibly previous stages, while protecting the supply.

By not blowing, the wirewounds protect the earlier driver stages but overload the supply, relying on the fuse for protection.

Actually, I would consider not changing the original resistors at all. Wirewounds are very tolerant of overloads, and if they did not actually melt or change value, they are as good as new.

[Ron Ramirez]

10-4. Sounds good to me. I'll still post a photo after awhile, but if I can keep the originals, then I will. Thanks very much, Mondial.

Edit: I never did apply full power - I was using a Variac, and cut the power at 60 volts when those resistors began to smoke.

[codefox1]

Are you sure you ae not going over to the "Dark side" by messing with Solid State?

[Ron Ramirez]

Naah, Codefox...I'm enjoying this...it's quite different from the hollow state Philcos of the 1930s.

[Ron Ramirez]

Okay, photos, as promised.

First, the two resistors in question. The yellow arrows in the photo points to the two resistors. The one on the right smoked, then the one on the left joined in as I was turning the Variac off.

[Image: http://www.philcoradio.com/images/phorum...0001-3.jpg]

Now, a close-up of one of the resistors (the one on the left in the photo above).

[Image: http://www.philcoradio.com/images/phorum...0002-3.jpg]