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PostPosted: May Mon 17, 2010 9:00 am 
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Location: Bloomington, Indiana, USA
Hi out there,

I re-worked an unlabeled, 26-volt transformer so that it is now powering a 26C6, which is a duplex diode-triode with a mu of 17.

I would like to make a simple regen as similar as possible to this 12K5 circuit. How do I change the circuit to feed the regen, since the 26C5 is just a triode and there is no other grid in the tube?

Tried the simplest thing I could think of, which was bringing the signal from the tank through a 2meg-ohm grid leak/270 pF cap, with a taste of the plate brought back around via potentiometer, but I can't seem to get the thing to oscillate.

After two hours on the bench trying different ideas all I can get is static. I can see the pot vary the waveform on the plate (there's a tiny bit of ripple in the DC which comes through), but I can't see even the tiniest bit of oscillation. I hear hisses and crackles and such from the little 8-ohm speaker as I work.

Note that I am trying the tube at 26.5 volts, same as the heater, which the RCA datasheet (dated June 20, 1946) claims works with a grid resistor of 2 meg-ohms.

Thanks in advance. I just can't seem to develop that 6th radio sense that tells a fella what to do.

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PostPosted: May Tue 18, 2010 5:36 am 
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So, er, that 26c6 works just fine in a simple regen circuit if one remembers to actually connect to ground. Ahem.

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PostPosted: May Tue 18, 2010 12:57 pm 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
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Location: Sandpoint, IDAHO 83864
If you could post a schematic of YOUR set here, we could pick it apart for you. Referencing back to someone elses circuit does not do any good, because like you said, you are using a triode and Norm was using a screen grid tube.

One of the major causes of a regenerative set not to oscillate is because the tickler coil is hooked up backwards. If the set refuses to oscillate, always reverse just the ticker coil leads and see if that helps. That is a number One rule when building regenerative sets.
Curt

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PostPosted: May Wed 19, 2010 10:29 pm 
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Thank you, sir,

I figured it out. I had not attached the bottom of the LC tank to ground, the instant that I did so, I could hear the local AM station. Apparently I had left the old philco variable and my coil tuned there from the last thing I made.

The 26C5 worked OK with 26 volts on the plate, but the sound on an 8-ohm speaker was weak b/c I had poor transformer matching. (The tran I have is 12:1 but the plate impedance on the 26C5 w/26 plate volts is 15500). Since right now I am just building circuits for practice until I get the "feel", I didn't forge ahead to try imepdance matching. Smith charts look like something I need to try when I grow up a little more. And I sure dont' have a 44:1 transformer.

Anyway, once I was satisfied that I "did it", I tore it apart and now have charged ahead with a different tube set. 6EJ7 feeding into a 25C5... my little salvaged transformer holds right at 29.6 volts with these two tubes cooking (600 mA). This time I'll put up a schematic and a pic in a new thread.

Thanks for your patience while I learn the ropes in the forum. This place is great.

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PostPosted: May Thu 20, 2010 6:12 pm 
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Hello Mike,
Wow looks like fun.

Rich


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PostPosted: Jul Tue 06, 2010 2:08 am 
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Location: Cambridge MN USA
At the risk of dragging this thread out even further, I've been in the process of getting parts together for one of these myself. Long ago there was a picture of one that was built onto the base of a container for CD blanks.

I decided to take that idea one step further and actually cut a piece of circuit board into the size of a CD and build the radio onto that. Unfortunately my bright ideas aren't always so bright. Got the outer part cut OK, but I don't have a 15mm punch for the center hole. Anyone able to help?

Scott


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PostPosted: Jul Tue 06, 2010 2:15 am 
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Uni-bit (step bit). The tinkerer's pal.

Actually they make some now that are smooth all the way instead of stepped. On something brittle that might work better.


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PostPosted: Jul Tue 06, 2010 7:48 am 
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I've actually used a spade bit to cut plastic with pretty good success. The two sharp outer cutters do all the work.

I cut perf board (which is usually fiberglass,I think) by clamping it to a 2x4. More brittle plastic I've cut by clamping it in sandwich of plywood scraps. I align the hole by drilling a small pilot hole, then running a wire through the wood and the plastic when I clamp it.

I have a unitbit, too, but it only goes to 7/8 so I have also used it as far as I can and then rounded out the remainder with a dremel and a sander. Don't forget that sometimes you can use a short post/standoff and machine screws to place the socket hovering 1/2" above the board. Sometimes that option works well.

Good luck with that regen! They're loads of fun. I love putting on the phones and then finding WWV. Seems like I only feel satisfied when I hear that steady ticking.

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PostPosted: Jul Tue 06, 2010 5:41 pm 
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Both for $15 at HF.

Image

http://www.harborfreight.com/2-piece-ti ... 96275.html


Last edited by Mike Toon on Jul Thu 08, 2010 12:05 am, edited 1 time in total.

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PostPosted: Jul Wed 07, 2010 10:46 pm 
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Now I need one of those!

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PostPosted: Jul Wed 07, 2010 11:25 pm 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
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Location: Sandpoint, IDAHO 83864
Just remember that south of the equator these things are made differently. The largest section is at the tip and the smallest section is where it chucks into the drill motor! HI!
Curt

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PostPosted: Jul Fri 09, 2010 12:50 am 
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Seems to me the diameter of the hole is 15mm. Do they make these in metric sizes?

Scott Todd


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 Post subject:
PostPosted: Jul Fri 09, 2010 6:01 pm 
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Location: Beautiful Downtown Burbank CA
15mm=.5905494"

.59375"=19/32"

Image

Sizes: 3/16" to 1/2" Six Step Bit (3/16", 1/4", 5/16", 3/8",7/16", 1/2")
1/4" to 3/4" Nine Step Bit (1/4", 5/16", 3/8", 7/16",1/2", 9/16",5/8",11/16",3/4")
1/8" to 1/2" Thirteen Step Bit (1/8", 5/32", 3/16", 7/32", 1/4", 9/32", 5/16", 11/32", 3/8", 13/32", 7/16", 15/32", 1/2")


Last edited by Mike Toon on Jul Tue 27, 2010 1:12 am, edited 1 time in total.

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 Post subject:
PostPosted: Jul Sat 10, 2010 3:53 am 
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Location: Austin, Texas
Ever since I bought a 3S4 regen kit on EGay and recapped and repaired a Knight Kit Span Master, I have been hooked on regen sets. Very sensitive and ALOT of fun to use:)-Gearhead


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 Post subject:
PostPosted: Jul Sat 10, 2010 11:41 am 
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Location: Portsmouth, Ohio
gearhead222 wrote:
EGay


You deserve a beer for that.


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 Post subject:
PostPosted: Jul Mon 26, 2010 10:24 pm 
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I don't see 19/32 on any of those uni-bits. I do have a regular one of those but they tend to produce a ragged hole and I'd like to avoid that if possible.

Scott


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 Post subject:
PostPosted: Jul Tue 27, 2010 1:05 am 
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N0BST wrote:
I don't see 19/32 on any of those uni-bits.

Scott
I was wrong.

Here's a set that's sure to please. Sizes: 3/16" to 1/2", 1/4" to 3/4", and 1/8" to 1/2"

Image

http://www.harborfreight.com/3-piece-st ... 66463.html


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 Post subject:
PostPosted: Apr Mon 18, 2011 1:01 pm 
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Location: Central Georgia
35Z5 wrote:
That was the 1st transformer I tried from a battery portable, wasn't very happy with it or one from a AA5...

Read through my posts in this thread, where I talk about the transformers I tried...

http://www.antiqueradios.com/forums/pos ... e&p=629058

Comments just after the picture and scope waveforms have the most info on transformers...

Tom


Now.... this is just plain weird.... when I open the link above, it goes to an open posting that is editable and, I assume, postable under Tom's name and pass word. Did he link to this post before actually posting it??? I've never seen this happen before.... :shock:

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 Post subject:
PostPosted: Apr Mon 18, 2011 4:52 pm 
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Tube Depot, in Nashville, Tn., has the 12K5 tube for $6.95, and they ship the same day. I bought some tubes from them on a Sunday, and the order was at my door on the following Wednesday. I ordered from Sheridan, Wyoming.The Tube Depot uses FEDEX, and they do not mess around. The Tube Depot ships the same day, if you order before noon{their time zone}


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PostPosted: Apr Mon 18, 2011 7:32 pm 
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Hi JG

I dunno what happened but I'd appreciate it if you edit out your link and I'll do same...

Thanks
Tom


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