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 Post subject: 6SN7 regen
PostPosted: Aug Mon 04, 2008 1:13 am 
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Joined: Aug Sun 03, 2008 3:59 pm
Posts: 16
Location: Bowling green KY
Hi all, I'm new to this forum, and relatively new to radio, in that I've been a licensed ham operator for just over a year, and have yet to make any on-air contacts. Homebrew Spirit (and total lack of funds) has kept me from getting any secondhand equipment, but I think I'll be fine with a regen and MOPA, at least for a while.

So, that aside, I'm currently building my third radio, hopefully the first one that works properly. I have a Regenerodyne, but have set it aside for the moment due to unsolvable selectivity problems. The superhet...well, don't ask. Double tuning was no problem, but the IF amp has me puzzled.

So this time, I've chosen the wildly popular 6SN7 regen as my "getting on the air" radio. It's a plug in coil design, for the AM BCB, 160M, 80M, and maybe 40M.

As for parts, I have a decent junkbox at my disposal. So far:

Three octal sockets
1 6SN7
1 12SN7
4 12L6
1 10EM7
Three octal bases (salvage from dud tubes)
1 AA5 tuning capacitor, with two ~25pF sections, 1 ~140pF section, and 1 ~300pF section. This is just eyeballing the thing, no actual measurements.
1 20pF air variable for bandspread, with 6:1 reduction vernier.
All kinds of magnet wire, from my transformer winding hobby
resistors and caps galore

And this schematic:

http://www.qsl.net/ab0cw/6sn7sch.gif

I am planning to leave the RF and detector stages alone, but would like input as far as the Audio section. Will the detector output be strong enough to drive a 12L6, or do I need another stage of gain, available from a 10EM7 or 6SN7 (can get more of anything, given enough time.)

Will I need a vernier drive on the main tuning cap, or just on the 20pF bandspread?

Any other suggestions for a successful radio?

Jake, KI4YAN


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 Post subject:
PostPosted: Aug Tue 05, 2008 6:15 am 
Member

Joined: May Tue 30, 2006 8:34 pm
Posts: 169
Location: Akershus, Norway
Hi Jake! :)
I believe you have enough gain there for an output tube. Since your winding transformers, why not make the output tranny yourself and add a tapping suited for your headphones?
I also believe that a vernier on the bandspread will do the job good.
Good luck! :)


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 Post subject:
PostPosted: Aug Wed 06, 2008 12:04 am 
New Member

Joined: Aug Sun 03, 2008 3:59 pm
Posts: 16
Location: Bowling green KY
Just finished winding the power transformer, 6.3V 1.5A and 150V, 90mA. Anyone interested in finding power transformers like this, take a good read at http://geek.scorpiorising.ca/windingtransformers.html

and pick up a Radioshack P/N 273-1511, a spool of #32 and #20 magnet wire, a roll of insulating tape (masking tape works well if you are going to be polyurethane-ing the windings, glass tape if not.)

Wind 35 turns of #20AWG enameled wire, leave plenty for connecting up the leads. Cut a strip of insulating tape, and wrap two full turns. Wind 830 turns of #32AWG enameled wire and tape again, two full turns. Leave plenty for leads later.

The remaining information needed for that power transformer in included in the link above, but all the math has been done and the wire fitted to the core here. Total cost: ~15$ if you only have to buy the transformer, not worth it unless you've got the wire already.

Hammond wants 22$ plus shipping for a comparable model from the 200 series...


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 Post subject:
PostPosted: Aug Wed 13, 2008 4:17 am 
New Member

Joined: Aug Sun 03, 2008 3:59 pm
Posts: 16
Location: Bowling green KY
Ok, so I got the chassis drilled and assembled tonight. Going to start construction of the regenerative and RF stages tonight, (power supply is done already) and see what I can do about coils...


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 Post subject:
PostPosted: Aug Wed 13, 2008 4:24 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 3667
Location: Circleville, OH, USA
Shouldn't the top of the 5K antenna input pot go to the grid rather than the cathode? The grid of the RF amplifier is floating in your diag.

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 Post subject:
PostPosted: Aug Thu 14, 2008 10:24 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 1643
Location: Watsonville, CA, US
Ken Owens wrote:
Shouldn't the top of the 5K antenna input pot go to the grid rather than the cathode? The grid of the RF amplifier is floating in your diag.


No, I think they are trying to make ground grid RF amp. They don't show the grid grounded but it should be. It looks like they are trying to jump a resisistor across the 5K pot. That should give about 2K between the ground and the Kathode, about right. By using such a lash up you get isolation between the antenna and the detector, a variable input attenuator, and the grounded grid approach is electronically very quiet.


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 Post subject:
PostPosted: Aug Fri 15, 2008 5:57 am 
New Member

Joined: Aug Sun 03, 2008 3:59 pm
Posts: 16
Location: Bowling green KY
Yes, it is a grounded grid RF amp. No, i didn't draw that diagram, nor did i follow it faithfully. Regen works great, just gotta get a new 6SN7...mine's a dud. got two new ones on the way, been using the 12SN7 with a separate heater supply to run the thing.

Next up is a transmitter for the ham bands, (160M so theoretically, i could retune for the BCB...)


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 Post subject:
PostPosted: Dec Thu 04, 2008 5:17 am 
Member

Joined: Jun Fri 27, 2008 3:10 am
Posts: 97
Location: Killingworth Connecticut 06419
Here is a 6SN7 regen and 117LGT Xmtr I built up for 160.

Also built up a one tube modulator and rcvr PS supply on the same type of "chassis".
Image
73
Carl
WA1KPD


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 Post subject:
PostPosted: Dec Fri 05, 2008 5:06 am 
Member
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1074
Location: Wayside, NJ Monmouth
They look great Carl. and so does your 2009 calendar. I hope top be working in the shop more this winter. And maybe I can make somthing a nice looking as yours. 73's de: Jeff N2LXM


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