1st question: Why is there a TV antenna connection point shown at the antenna??
2nd question:
It has a 6ae5 driving a 25ac5 for audio output.
Can someone knowledgeable here please try to give me a simple but clear explanation of how this cross coupled or cathode follower ...whatever.. works?
The plate of the 1st stage is connected directly to B+.
I get confused about bias and current flow as the cathode of the 1st stage is directly connected to the grid of the 2nd stage.
How does the thing work? From grid leak on the 2nd stage providing a reference to B- for the 1st stage cathode??
TheTV antenna thing means nothing, they wanted people to believe their radio was ready if and when TV ever happened.
The audio amp is something else!
The plate/cathode current of the first stage has to flow through the grid of the second stage, which has no bias.
This circuit will produce nothing but distortion.
There must be an error in the schematic.
Do you have this radio and can you trace the circuit?
No RCW... I don't own this radio yet.
I'm hoping to win it on Ebay.
But isn't there some sort-of a dual-triode? audio tube.. can't think of the number.. where this is done the same way but inside the tube?
Emerson DP332 uses a 6AE5GT as cathode follower driving the 25AC5. The 6AE5 gives no voltage gain but has isolation and current gain. It won't load down the incomming signal.
These tubes together are similar to 6B5, 6N6 and 25N6.
Best to add a resistor to ground where cathode of 6AE5 connectes to grid of 25AC5. Any leakage and the output tube can run away with current.
Norm
:::I'm looking at the schematic now for the possible purchase of an Emerson DP-332
:::http://www.nostalgiaair.org/PagesByModel/038/M0005038.pdf
:::
:::1st question: Why is there a TV antenna connection point shown at the antenna??
:::
:::
:::2nd question:
:::It has a 6ae5 driving a 25ac5 for audio output.
:::
:::Can someone knowledgeable here please try to give me a simple but clear explanation of how this cross coupled or cathode follower ...whatever.. works?
:::
:::The plate of the 1st stage is connected directly to B+.
:::I get confused about bias and current flow as the cathode of the 1st stage is directly connected to the grid of the 2nd stage.
:::How does the thing work? From grid leak on the 2nd stage providing a reference to B- for the 1st stage cathode??
:::
:::RCW
::
::TheTV antenna thing means nothing, they wanted people to believe their radio was ready if and when TV ever happened.
::
::The audio amp is something else!
::
::The plate/cathode current of the first stage has to flow through the grid of the second stage, which has no bias.
::
::This circuit will produce nothing but distortion.
::
::There must be an error in the schematic.
::
::Do you have this radio and can you trace the circuit?
::
:
:No RCW... I don't own this radio yet.
:I'm hoping to win it on Ebay.
:
:But isn't there some sort-of a dual-triode? audio tube.. can't think of the number.. where this is done the same way but inside the tube?
:
:
The cirucit is not messed up. This tube operates with positive bias as others here have mentioned. I have a pair of Emerson CS269's and they sound every bit as good as similar sets with a 25L6 output. I have a few 25AC5-GT RCA branded but are actually of Sylvania manufacture. RCA listed them as discontinued in the 1947 RC-15 tube manual but mysteriously are back in production in the 1950 RC-16 tube manual. The latest set I saw the 25AC5/6AE5 set up in was a Majestic T-711 from 1942.
Fred
RCWade,
In my 60 years in electronics I have completly missed this family of tubes!
It blows my mind to think of a tube with +14 volts bias, I can't understand the physics.....It seems to me the tube would be in complete saturation..
Can anyone here explain how this tube operates?
RC,
I first saw this type of circuit in Elements Of Radio Servicing Back in the mid 60's and they showed a Zenith 7S633 with a 6P5G driving a 6AC5G and like you it made no sense to me.
Every tube in that family seems to have a double grid, like a control and screen grid tied together. Looking at some 6N6Gs which have the cathode follower built in, they also have the double grid on the power triode section. Maybe someone here knows more of the physics involved.
The 6AC5 and 25AC5 have a high mu and if you look at the characteristics, they can be operated in class B push-pull although I never saw a set run them that way. If you want to see something even more confusing look up the Zenith 12S595Z which uses a pair of 6AC5Gs in push-pull dynamic coupled with a 6AE7GT which is a big single triode with a single large plate, one grid and two separate cathodes. Only three sets, a Motorola, and Emerson and the Zenith mentioned used it.
Fred
Fred R
RCW
See, this completely blows my theory that I knew everything...... well......maybe now I do!! (snicker)
RCW,
this blows my mind, in my many years of life in this world of electronic I have never seen an audio amp working with any kind of positive DC bias on the grid!!
I never heard of a 25AC5, but when I googled it just now it was mentioned a lot but I found nothing about how it works...
Basic electron tube operation is about modulating the electron flow from the cathode to the plate by a varying negitive voltage on the grid.
+14 volts on the grid??
If my hair wasn't already grey....well.
RCW:
Seems very strange to me too.... but..
Here is a link about it:
http://www.mif.pg.gda.pl/homepages/frank/sheets/127/2/25AC5GT
RCW:
Seems very strange to me too.... but..
Here is a link about it:
http://www.mif.pg.gda.pl/homepages/frank/sheets/127/2/25AC5GT
Data sheet shows this circuit as a cathode follower connected directly to grid of an output stage without bias resistor. Not a good idea. Any leakage and you can't guess what will happen.
Sylvania data books suggests a 25K resistor from this point to B-. They mention to prevent a surge while the tubes are warming up. The resistor does more than that. I would add this resistor even if the radio seems to operate right.
Norm
:http://www.mif.pg.gda.pl/homepages/frank/sheets/127/2/25AC5GT.pdf
All:
I constantly wonder why designers and engineers come up with these off-the-wall ideas like this tube. I suppose someone wants to show the world how smart he is by designing a circuit or a tube like this, but, in my opinion, all he does is make following generations of repairmen wonder "what was this fool smoking when he designed this circuit?" However, this comes from one (among others) that spent years trying to figure out the Lockheed L-1011 airplane and the thinking of the designers, where the above question was asked very often.
I am reminded of the time in literature class, when studying "The Rime of the Ancient Mariner" I said "He smokes dope and gets famous, we smoke dope and get busted." Not the wisest thing I did that day, fer sure.
Lewis