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 Post subject: 1G6 regen voltages?
PostPosted: Sep Tue 11, 2007 1:46 am 
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Anyone else notice this bottle requires a fairly high DC voltage ( 36vdc> ) to work at all as a regenerative detector? I'm trying one in a "Doerle" type circuit and was surprised that it needs 36 volts to regen. Only have 4 9-volt batteries in the set, I suspect the audio stage might work better with a higher voltage too. Anyone have any experience to share?

Pete


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 Post subject:
PostPosted: Sep Tue 11, 2007 2:32 am 
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Pete

1G6 was made as a class B amplifier. It require zero grid bias to operate with 90 volts on the plate. If you notice the plate is a long distance from filament. Radio will operate better with higher voltage. Even at 90 volts the plate only draws 1 ma.

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 Post subject:
PostPosted: Sep Tue 11, 2007 2:53 am 
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Norm

Is there a drop in replacement that might work better? I don't want to switch to 2 volt tubes like the 19. I noticed it was a class B audio and figured the 0 bias would be an issue!


Pete


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 Post subject:
PostPosted: Sep Tue 11, 2007 2:56 am 
Silent Key

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Try a 1J6.
Curt

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 Post subject: Reversed the filament battery..
PostPosted: Sep Tue 11, 2007 2:58 am 
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Running the A+ battery with the negative to the filament, positive to ground spruces it up a bit! Likes a bit of positive grid biasing via the cathode being made negative?

Pete

Norm: BTW, this is Bob Ryan's dumpster diver special...


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 Post subject:
PostPosted: Sep Tue 11, 2007 5:29 pm 
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Location: Tustin,CA
Hello,
My tube of choice for relatively low voltages (27-36 Vdc) is the 1G4, and to a lesser extent, the 1H4. Several years ago I got two NOS pairs of CEI and Sylvania 1G6GT's to turn my 1-tube 1G4GT regens into a Twinplex-type circuit using the 1G6GT. At those voltages, the detector gain was so low, that even adding the 2nd triode as an audio amp produced an overall gain less than one 1G4. That was true for all four tubes. I never tried higher plate voltages. I've not considered a 1G6GT since.
Dave, WA6VVL


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 Post subject:
PostPosted: Sep Tue 11, 2007 6:03 pm 
Silent Key

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Good Lord, look who shows up here! Dave- very nice to have you a member of the ARF. I hope you remember me, as we had quite a discussion several years ago about the VT-67 versus 30 tubes. It was after one of your many articles in Electric Radio Magazine.

I will have to vouch for Dave, if any of you other members have ever read some of his articles in ER, you will know he knows what he is talking about.

Again, Welcome aboard, Dave.
Curt

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 Post subject:
PostPosted: Sep Tue 11, 2007 6:29 pm 
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Pete

1J6, that Curt mentioned, is a little better but it's a 2 volt filament tube, like 19 but a different base.

Can you use higher B+ voltage? 1G6 is a higher gain tube than 1G4 but needs more plate voltage. It will make a nice 1 tube radio but requires 90 volts. No other directly interchangeable tubes.

Other dual triode battery tubes: 3B7, 3A5, 3C6

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 Post subject:
PostPosted: Sep Tue 11, 2007 8:16 pm 
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Hi Curt,

Yes, I do remember our conversation regarding the VT-67 vs 30. And, I have yet to run across a VT-67 that successfully works as a detector? I don't know what the differences are.

I have built a small number of 1-tube and 2-tube regens around the 1G4GT. The most ambitious was a 2-tube "Ultimate" SWL/Amateur receiver built around a 5-1/4" rack-panel. Most of the others are variations on a theme and are like the following 1-tube regen built into a baseball display case.

Image

I have also built several 19 Twinplex designs with and without the interstage xfmr. Now, when I build a 2-tube design, I will always add the interstage xfmr unless there's a real-estate problem. I have also built a display-case regen using the 957 acorn tube.

Dave - WA6VVL


Last edited by WA6VVL on Sep Thu 13, 2007 5:04 am, edited 3 times in total.

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 Post subject:
PostPosted: Sep Tue 11, 2007 9:28 pm 
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Reversing the battery filament voltage has made the difference. The set is working on 36 vdc with plenty of volume and the regen action is good.

Pete


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 Post subject:
PostPosted: Sep Tue 11, 2007 9:34 pm 
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Pete

Great, you probably have the grid slightly positive?

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 Post subject:
PostPosted: Sep Tue 11, 2007 9:59 pm 
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Norm Leal wrote:
Pete

Great, you probably have the grid slightly positive?


Hi Norm.. Yep, apparently reversing the A battery is providing positive grid bias and shifting the operating point nearer to the Class A region.

As you know, I'm using Bob's chassis, so the constraints are the existing tube socket, battery holder arrangements, etc. I didn't want to modify his physical layout too much. I did go to a 10K regen control for smoother action, and also have a 500 pF compression mica for a throttle cap. The throttle lets set the operating range for the 10K regen pot. I wish he had a few more 9-volt holders onboard, I'd be curious to see what more B+ might do, but it works fine as is.

Pete


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 Post subject:
PostPosted: Sep Sat 15, 2007 4:09 pm 
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I know that this is a dumb question. So installing a cathode resistor for negative grid bias is not the way to go? A more positive grid is better because of the weak signal voltage-in? Some time ago I had difficulty reversing heater polarity because my separate DC suppllies are sharing a common AC ground? When I reversed heater supply it knoched it-out. I will try again now that I see the benefits.

Got another question. Opperating a pentode one tube will have poorer detect because of two plate (screen/plate)? Better Q selectivity with triode?


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 Post subject:
PostPosted: Sep Sat 15, 2007 5:20 pm 
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tubeAMP wrote:
I know that this is a dumb question. So installing a cathode resistor for negative grid bias is not the way to go? A more positive grid is better because of the weak signal voltage-in? ?


Cathode bias is a very valid means to establish the tube's biasing. It can only provide negative bias, since it essentially makes the cathode more positive with relation to the control grid. Conversely, this means the control grid bias is negative to the cathode.

The 1C6 was designed for Class B operation with a relatively high 90 VDC B battery, and didn't require external biasing because of the grid placement relative to the plate and cathode.

When used in a regenerative with low battery voltages, the tube is almost running at cutoff, and in this rare instance some form of positive grid bias is needed to force the tube into a more linear region.

Reversing the battery voltage makes the filament/cathode more NEGATIVE than the grid (which is referenced to ground) providing a small amount of positive bias for the grid. It made a big difference in this application, which I must stress again is probably a very unique situation.

Pete


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 Post subject:
PostPosted: Sep Mon 17, 2007 1:29 pm 
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I see. So other tubes like the one Im using, 6V6 would not benefit by a more positive grid?


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 Post subject:
PostPosted: Sep Mon 17, 2007 9:06 pm 
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No, 6V6 requires negative grid bias. If the grid is zero or slightly positive on a 6V6 it draws a lot of current.

The 1G6 was designed to operate at zero grid bias and 90 plate volts. Pete was using low plate voltage so the 1G6 drew little plate current. 1G6 is only rated 1 ma @ 90 volts.

With a slightly positive grid the tube draws more plate current which is needed for operation.

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 Post subject:
PostPosted: Sep Mon 17, 2007 10:40 pm 
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I will have to try a cathode resistor to see what happens. Something small like 10 ohm :twisted:


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 Post subject:
PostPosted: Sep Wed 19, 2007 1:50 am 
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tubeAMP wrote:
I will have to try a cathode resistor to see what happens. Something small like 10 ohm :twisted:


If you're using cathode bias, you won't have enough bias on the 6V6 using a ten ohm resistor... Not a good thing.

Pete


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 Post subject:
PostPosted: Sep Wed 19, 2007 7:05 am 
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Hi

A 6V6 should have around 270 ohms as a cathode resistor. Bypass it with 10 - 25 mf @ 25 volts or greater cap. This will give proper bias and improve low frequency response.

Don't try operating with a positive grid on a 6V6.

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 Post subject:
PostPosted: Sep Wed 19, 2007 1:57 pm 
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You know we are talking about a one tube regen? I was thinking a small cathode resistor because of the small input and low plate voltage. Not usually working with formulas, Im just guessing. Thinking that normal opperation requires 270 ohm would this work with the tiny input signal?


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