Three Tube Regen

[Peter Heembrock]

I have put the Hallicrafters S-85 on hold for a while and will be attempting to build a three tube regen set using 01A tubes ( actually I will be using 01B tubes since they take half the filament current compared to a 01A’s so longer life on the A battery ). This one will be made mostly of vintage parts from some old 20’s AK sets with a few new parts being purchased/made. I wound a new coil for the RF front end and if this works I may try to use an old one…first things first. Ideally I want this to drive a RCA model 100A speaker ( hence the additional audio output stage ) since I do not like wearing high impedance headphones that are connected to 90VDC…

If all goes well I may put the guts in an old Ever Ready case…I will do this mostly in my spare time…which is pretty thin these days ( it is tax time now so that does require more of my attention ).

Peter H

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[John Greenland]

Peter;

Sounds interesting.
I am looking at building a TRF radio out of old and new technology , ( 6 / 12 SK7’s and varactor diodes as a start ) just to see if I can.

I am doing various bits of research on the best way way to build the coils / interstage transformers that I need.

Got any advice / hints to pass along ?

Thanks a bunch.

John G.

[Peter Heembrock]

Hi John,

I am assuming you are building one to operate in the AM broadcast band?
If so perhaps one thing that comes to mind based on my previous experience with rebuilding a few Atwater Kent sets from the late 1920’s is to keep in mind that the selectivity will vary depending on what part of the band you are on…this is based on the fixed Q of the coils in the RF section…I also read somewhere about other people having issues with this. Back in the day when these were used it was not too much of a problem because of the smaller number of AM broadcast stations.

The use of varactor diodes sounds interesting for sure in your design. The only other advise I can offer is use a metal chassis and if you are building this on a wood base to start with then be sure to use copper tape or single sided PC board to shield the RF components and help to stabilize/minimize stray capacitance.

Peter H

[John Greenland]

Peter;
Yes; staying in the AM band ( or lower) is the plan. I normally use a piece of plywood that I wrap in heavy gauge aluminum foil, as my base. It’s cheaper than spoiling an aluminum chassis. I like to start with octal tubes, as my sockets are OMROM 8 pin relay sockets. These are rated for 250 vac, and I have no interest in anything above 250 volts.

I do have a couple of homemade adapters for 7 and 9 pins. The 9 pin ones are only good for 12A— series tubes operating at 6 volts, however.

I was really wondering if you have any suggestions for coil design.
I am going to try a couple on 1/2 inch forms to start, but am open to any and all suggestions.
Thanks.
John G. VO1 CAT

[Peter Heembrock]

The 8 pin relay sockets are a good idea…I have a few of those that I recently picked up at Active Electronics…

Coil design will depend of course on the capacitance value that your varactor diodes are going to be operating at…typically what I have seen is a combo of 365pf along with an antenna coil assembly wound with about 100 turns on a 1 inch form…using a 1/2 inch form would require twice as many turns and the form may be quite long…but if you have the room for that it should be ok.

I do have some old coil forms on various sockets ( 4 pin, 5 pin etc )…but I chose to wind the coil for this radio on a 1 inch cardboard tube since it needs three sections.

I shuffled a few parts around on my set on the weekend so that the RF section is on the left and the AF section is on the right…not much overlap which is good…

PH

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[Peter Heembrock]

Pardon the mess but I decided to test the RF section last night so I hooked it up with many fly wires …

It actually worked first time and I now understand how tricky these can be to tune sometimes…of course I wired the regen pot up backwards which did not help. With my resonant loop antenna hooked up and a pair of headphones connected to where the inter stage transformer would be I found the volume to be quite loud…which is great since driving a speaker with the two tube AF section will probably most likely work now.

I do have to put dome aluminum tape or copper circuit board on the front panel since tuning is difficult due to the affects of stray capacitance from my hand.

The four 201B tubes I have on hand all performed well when I tested each one in the RF section…

Peter H

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[phil]

A very impressive and interesting project Peter.

If you want to daisy chain 9V cells and easy trick is to save the ends of old 9V cells, then you can use them as connectors to tie them together. maybe its just an obvious “trick”. I’m sure I wasn’t’ the first with the idea or anything.

I was sitting in my armchair one day and heard a loud “bang” – a 9V battery had been sitting on my end table and when I threw down my keys it had shorted and the heat of the cell blew the bottom cap across the room. ever since I look at the battery recycle bins and wonder if that ever happens because they contain a whole lot of batteries, surely some have a charge still.
I sometimes save the little clips when I dispose of dead 9V cells. they are handy connectors.

Phil

[Peter Heembrock]

I am currently using new 9V battery clip and wire assemblies that I picked up at Active…pretty cheap these days and it helps me here since I need 67 volts for the RF tube and pre amp tube and 90 volts for the final output stage…I can just tap off the battery string for the 67 volts quite easily. I added some copper tape last night on the back side of the front panel and that certainly helps with the tuning…it is so cool to hear a weak station and then just by turning up the regeneration pot it becomes very loud..then breaks into oscillation if I go too far.

My next step is to redo the RF stage wiring ( clean it up ) and then hook up the other two 201B tubes for the AF section so I can hear it on my RCA 100B…and it should be quite loud I think…and then it will go into the Everyready wooden box I have kicking around just to see if it will fit etc…then I can listen to the Toronto Blue Jays this year…and hopefully they can get closer to the finish line…

PH

[Jean Marcotte]

Hi Peter,

when I restored a Westinghouse RC for the International Restoration Contest in 2015, I tried various plate voltages for both the detector and the audio and ended-up with all three tubes working on 27 volts. That was well enough to drive the speaker and I had less noise in the set. Normal voltages would have been 22.5V for the detector and 45V on the two audio tubes. Even 18V give adequate results but with less volume. The whole story is here :

https://sqcra.org/wp-content/uploads/2015/04/2015_CRI_SQCRA_westinghouse-RC.pdf

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[Peter Heembrock]

Very impressive Jean…nice job on that restoration. I see the mice loved it as well…yikes!

The set I am building is based off of the AK model 30, 33 and 49…I have one of each of those and have restored them to be fully operational…I use my RCA 100A speaker when I listen to them. I like using the 201B tubes in this design since they use only 125mA for the filament current compared to 250mA for the 201A tubes. I am also using the regenerative coil design from a Hiker’s 1 radio project and it seems to work well. This is kind of a mish mash of sorts and when it is all finished and cleaned up then I will certainly revisit the plate supply voltages and look at the published curves for these tubes and see where I stand…thanks for sharing your restoration project…again that looks awesome.

Peter H

[Peter Heembrock]

All done for now…finished off the AF section and cleaned up the wiring in the RF section. This set works well and has good volume on the speaker and is quite clear. Tuning works well and the regen control works as it should…it does increase the volume quite a bit after you tune in a station…then of course one hits the oscillation point…

I will use my scope next and see how low I can go on the plate voltages while still maintaining proper operation ( I am running them at 67 volts right now…)

PH

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[Jean Marcotte]

Pete,

two audio stages and only one transfo ?

Jean

[Peter Heembrock]

Yup…last stage is RC coupled since I do not have two inter stage transformers in my junk bin…once I look at the levels with my scope I will decide what to do ( dig around for another inter stage transformer or hack two audio output transformers together… hopefully one has a center tap so I get a bit of voltage gain through it…will see…I am leaving it for now and working on fixing up the Eveready wooden case for it…

PH

[Ed Kraushar]

A workable transformer can be found in an old dial (500 type) telephone. It must be the dial type from the 50’s up that has an actual bell in it. The bell ringer has a coil that will work quite well as a 2 1/3 to 3:1 interstage transformer. I stress the bell assembly, not the network assembly potted in a shell.

These phones are getting hard to find now. I used to pick up old damaged or marked up ones from flea market, phones that they could not sell. I have used them many times in 20’s radios, usually disguised in some sort of shell.

Ed.

• This reply was modified 1 year, 7 months ago by Ed Kraushar.

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[phil]

I have what I think is a kit radio available perhaps from a magazine but never completed?
I promised Peter I’d send photos of it. I will just make a post about the radio parts I have. Maybe readers of this post could also take a look.

Phil

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