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 Post subject: Re: Help with Zenith amp Phase Inverter & rectifier tube typ
PostPosted: Mar Sat 30, 2019 9:48 pm 
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Vintage Collector wrote:
DrRick wrote:
First thing I would add is a fuse!
Perhaps I missed one in the schematic, I only glanced at it for a moment.

I once subbed a 5U4 for a 5AR4 in a nice EL84 PP stereo power amp. I knew it required an extra amp for the filament, but it was intended only as a test. I had planned to use a 5R4 and add a fuse.
It sounded so nice I listened to it for a couple of hours.
Then it had no sound at all. Shorted power transformer. I didn't think it would happen so quickly!

Best of luck on your project.

Rick


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! :shock:

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.

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 Post subject: Re: Help with Zenith amp Phase Inverter & rectifier tube typ
PostPosted: Mar Sun 31, 2019 5:59 am 
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Vintage Collector wrote:
westcoastjohn wrote:
Right, the engineers would never come up with a circuit that increased hum. Looking at the schematic, the input is on its own winding, not on the power input winding. That is a hum-bucking circuit by the looks of it. Another reason to take care of the transformer, as you won't easily find that winding in a replacement.


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. 8)

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 Post subject: Re: Help with Zenith amp Phase Inverter & rectifier tube typ
PostPosted: Mar Sun 31, 2019 11:08 am 
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westcoastjohn wrote:
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. 8)


Thanks! I hope everything turns out to be fine once I get it fired up.

I've on of these output transformers with me. It a 25W new sensor corp. NSC-41318-T transformer.

https://www.worthpoint.com/worthopedia/ ... -149157870

What do you think about this? Will it work fine?

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 Post subject: Re: Help with Zenith amp Phase Inverter & rectifier tube typ
PostPosted: Mar Sun 31, 2019 8:44 pm 
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That output transformer will work on this amplifier provided you use an 8Ω speaker with it.

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 Post subject: Re: Help with Zenith amp Phase Inverter & rectifier tube typ
PostPosted: Apr Tue 02, 2019 6:22 am 
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Mr. Detrola wrote:
That output transformer will work on this amplifier provided you use an 8Ω speaker with it.



Thanks! I plan to run it with a Zenith 7" 8 ohm speaker.

Also if I ran two speakers in parallel it would become a 4 ohm configuration right?

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 Post subject: Re: Help with Zenith amp Phase Inverter & rectifier tube typ
PostPosted: Apr Tue 02, 2019 5:08 pm 
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Vintage Collector wrote:
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


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 Post subject: Re: Help with Zenith amp Phase Inverter & rectifier tube typ
PostPosted: Apr Tue 02, 2019 5:50 pm 
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SparkyDan wrote:
Vintage Collector wrote:
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


Thank you so much Dan for pointing that out! Jesus!! How did I miss it on the schematics:!: ..I'm glad that my 5Y3 tube delivery was delayed till tomorrow.Or powering its up and my audio source goes poof!

So, the audio from the pre-amp output has to go to Pin 5 and the ground right? What are the other pins 4&6 for? Also I've only recently started to get more into tube electronics only. I was more of a solid state guy. I've one of these ECC83 pre-amps with me which I use with my Pilot tube tuner. Can I connect from the output of this to the pin 5 & GND or do I need to make some mods?

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 Post subject: Re: Help with Zenith amp Phase Inverter & rectifier tube typ
PostPosted: Apr Tue 02, 2019 6:15 pm 
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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


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 Post subject: Re: Help with Zenith amp Phase Inverter & rectifier tube typ
PostPosted: Apr Tue 02, 2019 6:39 pm 
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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


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 Post subject: Re: Help with Zenith amp Phase Inverter & rectifier tube typ
PostPosted: Apr Tue 02, 2019 7:48 pm 
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SparkyDan wrote:
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


Yes, I plan to keep the pilot light connection disconnected. Its a 6.3V circuit so maybe could be used for a tube filament in the future. Anyway I plan to not use it at the moment. I plan to use the RCA jack for input.

Pardon me, but I didn't understand what you are trying to say here "The output from the Pilotuner is at line-level voltage, and would go to pin 5 as well." My tuner is a Pilot FA-540. The audio output is from a 12AU7 cathode follower. It's output is pretty weak and would need the Power amp to be run pretty high to get any playback. This is why I used the ECC83 pre-amp with the Pilot tuner. Here is link to the google drive with the schematics in case you want to check it out:

https://drive.google.com/file/d/1xo46os56NFXExN8yzOsYG7IbbbUCAbzj/view?usp=sharing

I plan to use only the AUX Amp output. The Phono output is left idle. I've replace all the film capacitors as of now. Just waiting for the electrolytics to arrive that I had ordered.

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 Post subject: Re: Help with Zenith amp Phase Inverter & rectifier tube typ
PostPosted: Apr Tue 02, 2019 7:54 pm 
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SparkyDan wrote:
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


Yes, I saw from the schematics that the volume and Tone controls are just buttons. I was thinking that first I needed to figure out to get this working first. If things went fine then the next step is to get help from you guys and add a Volume pot and a tone pot for Treble/Bass.

No need for apologies buddy. Feel free to ask anything, I'm planning to run only the Aux input from the tuner via my phone or iPod for playing mp3 music at the moment so that I have value control.

Well as for the radio it doesn't have any volume control. This tuner has a pre-amp and power amp unit which has the afore mentioned controls but I didn't buy it since it was way expensive. I could control the audio output gain via the "Level Set" pot on the Pilot tuner though.

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 Post subject: Re: Help with Zenith amp Phase Inverter & rectifier tube typ
PostPosted: Apr Wed 03, 2019 4:20 am 
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Hello Dan,

Wanted to give an update. I've changed the connections as of now. I had taken out the transformer to remove the rust and spray paint it. Something. also noticed was that the filaments of the 6V6 and the 6C4 were connected to the same 6.3VAC on the RCA jack. Now the RCA jack is only connected to the Pin 5.

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 Post subject: Re: Help with Zenith amp Phase Inverter & rectifier tube typ
PostPosted: Apr Thu 04, 2019 2:09 am 
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Hello again, Vintage. One note of caution - - - don't attempt to power up your amp without an output transformer present & speaker connected. Tubes amps need to see the load they were designed for. Patience is a virtue . . . . .

Dan


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 Post subject: Re: Help with Zenith amp Phase Inverter & rectifier tube typ
PostPosted: Apr Thu 04, 2019 4:11 am 
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Noted! I'll power this up again only once I get it fully assembled and ready to run :)

What do you think about the addition of Volume and Tone controls?

--Raul

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 Post subject: Re: Help with Zenith amp Phase Inverter & rectifier tube typ
PostPosted: Apr Fri 05, 2019 3:13 pm 
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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


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 Post subject: Re: Help with Zenith amp Phase Inverter & rectifier tube typ
PostPosted: Apr Mon 08, 2019 6:14 am 
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SparkyDan wrote:
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


The pre-amp circuit I had posted prior is already a separate unit. It was obtained from a German EMUD 713ST phono-radio(picture below). Originally it was supposed to use a ECC83/12AX7 but later I had to stick with a 5751 since that was only what I had with me.

The compact size of the power amp is th reason why I decided not to add any pre-amp stage and there is a big possibility of hum like you mentioned due to coupling. This is one thing I'm trying to figure out where I should place the audio transformer It would have been nice if I could it on the top if the chassis itself. Thinking if I should get rid of the can cap and play the output transformer there :?:

This EMUD pre-amp requires a 240VDC power supply. That is not an issue since I already have a 210VDC supply for the preamp I made using a 6X4W.


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