Hi Rick,

Yes, I wanted to add a fuse.A little bit of googling shows the transformer MODEL (95-921 100 watts) is 340-0-340 @ 95ma, 5V @ 2A , and 6.3V @2.5A.

Yeah, these transformers aren't so forgiving at times especially if its more than 500mA if run for a long time. For few hours!

I would never run it for that long unless I was dead sure the transformer can handle it. I have already ordered an NOS 5Y3GT. I do have a couple of power transformers. But here in my case a short transformer is extremely bad news! As you have seen in the below comments mentioned by westcoastjohn. The input winding is within the power transformer itself. Also the amp is so tightly packed that unless I mount a audio output transformer on the sides there is no way. That would look pretty ugly!

Thanks, I've also ordered the 6C4. So, the only thing now I'm waiting to confirm is the type of audio output transformer that I should use.

Yes, from the circuit I saw that it is a separate winding. Sorry, if my. question wasn't precise. But wouldn't the 60Hz from the line intrude a hum to the input coil. Since its coupled on to the power transformer?

I'll not put this to full use until I get all the required tubes and audio output transformers and verify its ready for everyday use.

I think, most likely, that other winding on the primary side is either out of phase or wound in the opposite direction so that hum is canceled. Anyway, you will soon get a chance to try it out. Good luck.

That output transformer will work on this amplifier provided you use an 8Ω speaker with it.

Also one thing that bugged me from the beginning is that the input RCA jack is connected to the green-green wire on the primary side of the power transformer. Wouldn't this cause the hum and other noise to be introduced this way rather than a separate input audio transformer ?

That RCA connector is for a #44 Pilot light, not the audio input!!! The audio input is pin #5 on the connector.

Dan

Pin 4 & 6 supplied B+ voltage to the rest of the radio/tuner. Pin #5 & GND would be your input - - you might wire them to an RCA jack for convenience. (I strongly recommend disconnecting the "pilot" power; too easy to make a plug-in mistake! Maybe you could use it for the input instead.) The output from the Pilotuner is at line-level voltage, and would go to pin 5 as well. As far as the preamp - - - the RCA jacks may provide enough signal to drive the amp, but would only work if you had a phono/cartridge as the input source. The terminals labeled "Aux Amp" would provide a higher signal level - from any of the preamp inputs - but it might possibly be too much. You could calculate it, but just trying it out is easier! If it hasn't been mentioned before, it would be wise to replace the coupling caps in the amp before proceeding further.

Dan

One more thing - - that preamp is a linear amp circuit - - no volume or bass/treble controls. The power amp is the same way - full power all the time. You're going to need an input source that has these controls. Apologies if I'm telling you something you already know!

Dan

I think you'd be happier with a stand-alone preamp, with multiple switchable inputs. Dynaco, Eico and Heathkit all made simple preamps that worked well. You could possibly add-on to the Zenith amp chassis, but due to it's compact size, you might run into shielding/hum problems, especially if you wanted to use a phono input source - - which you'd need another amplification stage for. The RCA tube manuals have a few decent circuits included in the manuals as well. You could build one of these preamps, and connect it to the amp with a cable to the existing socket. Since the Zenith already has a b+ power supply, as well as a 6v. filament supply, your preamp could easily run off of it. Fabricating a connecting cable wouldn't be too difficult.

Dan