Triode Comparison and best Pentode for regenerative detector - UK Vintage Radio Repair and Restoration Discussion Forum

Neil Purling · 19th Apr 2008, 5:24 pm

The gain of the 6J5 and the triode sections of a 6Q7 and EBC33:
How do they compare?
The 6J5/6Q7 or EBC33 is going to be the first AF stage to drive a 6V6.
The signal source may be either a EF36, ME1400 or EF39 used as a regenerative detector.
I have cut no metal yet so perhaps you might reccomend another valve as providing smoother regeneration. I rejected a 6K7, which is a little out of it's depth here. Do the likes of the EF80 and EF91 still have too high a slope?

It is possible you might have a unusual choice, as long as it's got a 6.3V heater I will consider it for the electron coupled circuit.

jjl · 19th Apr 2008, 7:42 pm

Hello Neil

Duncanamps TDSL here

http://tdsl.duncanamps.com/tubesearch.php

should be able to supply all the data you need. In brief, the 6J5 appears to have very similar characteristics to half of an ECC82 / 12AU7 / 6SN7 with a mu of around 17. The EBC33 triode has a mu of 33. The 6Q7 triode has a mu of 70.

Hope this helps.

John

OErjan_S · 19th Apr 2008, 8:45 pm

the 6SK7 works ok in my paraset, but as it is more or less same as 6K7 it is not the desired answer (pinout is main difference).
I have ok experience with 6AU6 and 6BA6 in simple regens,to bad about that 6V requirement it narows the field.
if we step outside that I have found 1H4, 1S4 (DL91) , 3S4 (DL92) to be good regen tubes.

Neil Purling · 19th Apr 2008, 8:59 pm

I culled the AF amplifier circuit from Radio for Boys by E.N. Bradley C1952. It came with included mistakes, which the members of this forum were kind enough to pint out.
It was the audio end of a mains 4 valve superhet and used a EBC33 & 6V6.
The virtue of it is that even today the 6V6 is a very common valve. Forum members came up with 'G' envelope 6V6's when I asked.
I used the 6J5 triode because it was what I could get at the time and it is sounds like I ought to have used the triode part of a EBC33 or 6Q7.

I was told that a 'weak' type of RF pentode would give much more controllable regeneration. I had been looking for gain in the wrong place you see, and high slope types were not the answer. Something like a EF36, 37 or at the outside a EF39, although I have not been able to asses a variety of new examples of the types to see if my initial findings are true of all examples of the same type of valve. I have a NOS EF36 by Rogers of Canada, a pair of Mullard ME1400s that are a variant of a EF37a and a unidentified ex MOD EF39 bearing the post WWII CV code. That was a new valve too.

I have had a whole heap of fun along the way. I found that despite using (small) modern 22 + 47uf as reservoir & smoothing on the HT line I was still getting 20 volts of ripple, despite using a choke between the two capacitors.
A 'scope is a great tool. With it I was able to see the strength of the signal input and set a signal generator to give the same output level so I could make proper tests with a steady signal input. I know where the hum problem is coming from and so I have ordered new capacitors, which I believe have a much better ripple rating.

It looks like I have got some more interesting experimentation to come!

OErjan_S · 20th Apr 2008, 10:29 am

yes indeed, the "experimenting" is my main reason fot this hobby (something to do in a loooong dark winter night)

paulsherwin · 20th Apr 2008, 10:42 am

The EF36, EF37 and EF39 all have the same pinout so it is easy to experiment. (Many other small signal octal pentodes use this pinout too, including the 6K7).

The audio triode won't be at all critical. A higher slope valve will give more gain but you probably won't notice it in this sort of circuit.

Paul

Skywave · 20th Apr 2008, 2:52 pm

For a regenerative detector, a valve with a low gm is the preferred choice - such as the 6BR7.

Al / Skywave.

Neil Purling · 20th Apr 2008, 4:44 pm

I note the 6BR7 is not a Octal based valve, but the gm is quite low as you say.
Has anyone used this valve as a detector & had hum issues?

paulsherwin · 20th Apr 2008, 5:36 pm

The 6BR7 was specifically designed to have low hum pickup so I wouldn't expect this to be a problem.

The EF36 also has a fairly low gm, though not as low as a 6BR7.

Paul

Neil Purling · 20th Apr 2008, 7:52 pm

OK I will give that a try. It is a CV4006 actually. This is a military spec version of a 6059, which in turn is a special quality version of the 6BR7.
The pin diagram of the CV4006 mentions a inter-electrode screen on pins 1&6. To be connected to chassis obviously.

19th Apr 2008, 5:24 pm	#1
Neil Purling Nonode Join Date: Jul 2005 Location: Hull, East Yorkshire, UK. Posts: 2,087	Triode Comparison and best Pentode for regenerative detector The gain of the 6J5 and the triode sections of a 6Q7 and EBC33: How do they compare? The 6J5/6Q7 or EBC33 is going to be the first AF stage to drive a 6V6. The signal source may be either a EF36, ME1400 or EF39 used as a regenerative detector. I have cut no metal yet so perhaps you might reccomend another valve as providing smoother regeneration. I rejected a 6K7, which is a little out of it's depth here. Do the likes of the EF80 and EF91 still have too high a slope? It is possible you might have a unusual choice, as long as it's got a 6.3V heater I will consider it for the electron coupled circuit.

19th Apr 2008, 7:42 pm	#2
jjl Octode Join Date: Jan 2003 Location: Ware, Herts. UK. Posts: 1,082	Re: Triode Comparison and best Pentode for regenerative detector Hello Neil Duncanamps TDSL here http://tdsl.duncanamps.com/tubesearch.php should be able to supply all the data you need. In brief, the 6J5 appears to have very similar characteristics to half of an ECC82 / 12AU7 / 6SN7 with a mu of around 17. The EBC33 triode has a mu of 33. The 6Q7 triode has a mu of 70. Hope this helps. John

19th Apr 2008, 8:45 pm	#3
OErjan_S Retired Dormant Member Join Date: Mar 2007 Location: Skelleftea, Sweden Posts: 250	Re: Triode Comparison and best Pentode for regenerative detector the 6SK7 works ok in my paraset, but as it is more or less same as 6K7 it is not the desired answer (pinout is main difference). I have ok experience with 6AU6 and 6BA6 in simple regens,to bad about that 6V requirement it narows the field. if we step outside that I have found 1H4, 1S4 (DL91) , 3S4 (DL92) to be good regen tubes.

19th Apr 2008, 8:59 pm	#4
Neil Purling Nonode Join Date: Jul 2005 Location: Hull, East Yorkshire, UK. Posts: 2,087	Re: Triode Comparison and best Pentode for regenerative detector I culled the AF amplifier circuit from Radio for Boys by E.N. Bradley C1952. It came with included mistakes, which the members of this forum were kind enough to pint out. It was the audio end of a mains 4 valve superhet and used a EBC33 & 6V6. The virtue of it is that even today the 6V6 is a very common valve. Forum members came up with 'G' envelope 6V6's when I asked. I used the 6J5 triode because it was what I could get at the time and it is sounds like I ought to have used the triode part of a EBC33 or 6Q7. I was told that a 'weak' type of RF pentode would give much more controllable regeneration. I had been looking for gain in the wrong place you see, and high slope types were not the answer. Something like a EF36, 37 or at the outside a EF39, although I have not been able to asses a variety of new examples of the types to see if my initial findings are true of all examples of the same type of valve. I have a NOS EF36 by Rogers of Canada, a pair of Mullard ME1400s that are a variant of a EF37a and a unidentified ex MOD EF39 bearing the post WWII CV code. That was a new valve too. I have had a whole heap of fun along the way. I found that despite using (small) modern 22 + 47uf as reservoir & smoothing on the HT line I was still getting 20 volts of ripple, despite using a choke between the two capacitors. A 'scope is a great tool. With it I was able to see the strength of the signal input and set a signal generator to give the same output level so I could make proper tests with a steady signal input. I know where the hum problem is coming from and so I have ordered new capacitors, which I believe have a much better ripple rating. It looks like I have got some more interesting experimentation to come!

20th Apr 2008, 10:29 am	#5
OErjan_S Retired Dormant Member Join Date: Mar 2007 Location: Skelleftea, Sweden Posts: 250	Re: Triode Comparison and best Pentode for regenerative detector yes indeed, the "experimenting" is my main reason fot this hobby (something to do in a loooong dark winter night)

20th Apr 2008, 10:42 am	#6
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,966	Re: Triode Comparison and best Pentode for regenerative detector The EF36, EF37 and EF39 all have the same pinout so it is easy to experiment. (Many other small signal octal pentodes use this pinout too, including the 6K7). The audio triode won't be at all critical. A higher slope valve will give more gain but you probably won't notice it in this sort of circuit. Paul

20th Apr 2008, 2:52 pm	#7
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Triode Comparison and best Pentode for regenerative detector For a regenerative detector, a valve with a low gm is the preferred choice - such as the 6BR7. Al / Skywave.

20th Apr 2008, 4:44 pm	#8
Neil Purling Nonode Join Date: Jul 2005 Location: Hull, East Yorkshire, UK. Posts: 2,087	Re: Triode Comparison and best Pentode for regenerative detector I note the 6BR7 is not a Octal based valve, but the gm is quite low as you say. Has anyone used this valve as a detector & had hum issues?

20th Apr 2008, 5:36 pm	#9
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,966	Re: Triode Comparison and best Pentode for regenerative detector The 6BR7 was specifically designed to have low hum pickup so I wouldn't expect this to be a problem. The EF36 also has a fairly low gm, though not as low as a 6BR7. Paul

20th Apr 2008, 7:52 pm	#10
Neil Purling Nonode Join Date: Jul 2005 Location: Hull, East Yorkshire, UK. Posts: 2,087	Re: Triode Comparison and best Pentode for regenerative detector OK I will give that a try. It is a CV4006 actually. This is a military spec version of a 6059, which in turn is a special quality version of the 6BR7. The pin diagram of the CV4006 mentions a inter-electrode screen on pins 1&6. To be connected to chassis obviously.