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 Post subject: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Mon 27, 2019 2:39 am 
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Was there ever a RF Pentode with a 2.5V indirect heater and a UY base? The 39 is an UY based RF Pentode but has a 6.3V filament. A 58 is also an RF Pentode with a 2.5V filament but uses a 6 pin base. I have an RCA document that mentions an unnamed UY based RF Pentode in 1931. Most likely it was a prototype tube, but it doesn't seem like anything that ever became commercially available.

Darryl


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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Mon 27, 2019 4:44 am 
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I am reasonably sure there was not. The only 5 pin pentode with 2.5 volt filament I know was the audio amplifier type 47. I searched for anything similar, and I found one equivalent,
--edit: Champion 704. The only others close were the 6 pin 58 RF tube and 2A5 amplifier
--2nd edit: that should be Champion P704. It was supposed to be the equivalent of a 47.


Last edited by tubemaster on May Tue 28, 2019 5:35 am, edited 2 times in total.

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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Mon 27, 2019 5:36 am 
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Well, there is the one offered at the link below but it did not come in to common use.

viewtopic.php?f=15&t=334120

Norman

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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Mon 27, 2019 12:12 pm 
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I can't stop wondering, why do you want an RF amplifier with indirectly heated cathode with 2.5 volt heater, and need to use a 5 pin base?

The other question, is a P-1 an RF amplifier? Where was it used?

John


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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Mon 27, 2019 12:20 pm 
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The P1 is an RF amplifier, or possibly and IF amplifier if used in a Superhet.

It was only used by home builders as I doubt any manufacturer would have used it with the 800 pound gorilla (RCA) in the room.

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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Mon 27, 2019 2:25 pm 
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Thanks for all the replies.

John, I wasn't familiar with the 704. This appears to be a very odd pentode with no control grid cap. I should have mentioned that the RCA tube did have the control grid going to a cap.

Norman, I had never heard of the P-1. Quite the odd tube with the suppressor grid brought out to a binding post rather than just connected to the cathode.

John, this was in reference to a 1931 RCA document on television development where a receiver is described as using a 227, several 224's and two RF pentodes for the IF's without giving any more information. All tubes were lit from the same 2.5VAC supply and the unknown tubes used UY bases with grid caps. I'm assuming since the other tube numbers were listed and these weren't they must have been some prototype tube very similar to the 39 with a 2.5 filament or a 58 stuck in a UY base with the suppressor grid tied to the cathode.

Darryl


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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Mon 27, 2019 3:26 pm 
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tubesrule wrote:
I have an RCA document that mentions an unnamed UY based RF Pentode in 1931. Most likely it was a prototype tube, but it doesn't seem like anything that ever became commercially available.


Maybe RCA had something like the 1930 Ce-Co P1 RF "AC Pentode" tube in mind. It does have a UY base but it also has an extra connector on the side of the base shell. Only a small amount of these tubes were ever made and, today, their considered to be an extremely rare tube to find. Those that are found tend to be NIB. Only Ce-Co made this type of tube in the US.

Image
http://www.indianaradios.com/Norden%20H ... ceiver.htm

http://www.indianaradios.com/CeCo%20P-1 ... 20Tube.htm

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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Mon 27, 2019 4:49 pm 
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The CeCo P-1 was used in a Norden Hauck receiver, the DX-5, I believe.


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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Mon 27, 2019 10:04 pm 
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You guys have solved it!

The P-1 must be very similar to what RCA used. I just remembered that the two IF's in question had what I thought were some sort of test points in them, but they were obviously for the extra pin on the side of the base. Notice the two IF UY sockets on the left and two normal UY sockets on the right for the 224's.
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Those leaf pins on the left sockets are at about 20V above the cathode which is what the P-1 shows for the "space charge grid" so this absolutely is what they must have been using. The indexing on these sockets looks different than the P-1 as the P-1 shows the post centered between the 4 pins whereas RCA has it between the odd pin and group of four, so the P-1 is not a direct plugin. Unless someone knows of RCA using a system like this before the P-1, it would seem they "borrowed" the idea from CeCo.

Which brings up another question, the P-1 is not what I would think of as a typical pentode where a suppressor grid was placed between the screen grid and the plate and typically connected to the cathode. This pentode is a standard tetrode with a "space charge" grid placed around the cathode according to the literature. So the P-1 appears to actually be just like the space charge tubes of the late 50's early 60's used in car radios?

Darryl


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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Tue 28, 2019 1:10 am 
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Drakes 1922
Attachment:
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SPACE CHARGE PENTODE  TYPE 12K5  WITH 145 OHMS PLATE RESISTANCE.jpg
SPACE CHARGE PENTODE TYPE 12K5 WITH 145 OHMS PLATE RESISTANCE.jpg [ 166.96 KiB | Viewed 312 times ]

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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Tue 28, 2019 1:34 am 
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Steve,
The second document you posted showing the pentode looks like the exact fit. The voltages and pinout are all correct as is the position of the extra pin. What tube is this?

BTW the voltages on one of these tubes calculate to:
cathode: 0V
space charge grid: 16V
control grid: -1V
screen grid: 104V
plate: 232V

Darryl


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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Tue 28, 2019 2:56 am 
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Drakes Radio Cyclopedia - cool book.


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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Tue 28, 2019 3:27 am 
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Location: Cedar Rapids, Iowa, USA
Darryl, can you tell us more about the 1931 RCA TV document? Like was it an internal doc, or published somewhere? It would seem very plausible to me that RCA would want to develop a new, unique tube for one of their (then) cutting-edge new systems.

John


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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Tue 28, 2019 3:57 am 
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John,
There was a set of four IRE papers that RCA delivered on the set that can be found here:

http://www.earlytelevision.org/pdf/experimental_tv_system.pdf
http://www.earlytelevision.org/pdf/rca_experimental_receiver.pdf
http://www.earlytelevision.org/pdf/rca_experimental_xmtr.pdf
http://www.earlytelevision.org/pdf/experimental_tv_and_kinescope.pdf

It can be seen in the partial schematics and text above that the tubes are all shown as tetrodes and most are called out specifically as 224's with the IF's not specified so I had assumed they were 235's or similar. The internal document describes the picture receiver as: "utilizing one 227, six 224's and two pentodes" but doesn't specify anything beyond that. Strangely, they used a prototype R-601 HV rectifier that they did call out in the power supply, so it's odd why they didn't say anything more about the pentodes.

Realizing now that the extra contacts on those two sockets had to be for the extra grid post on the side of the base and looking at the voltages, the P-1 style space charge pentode is an exact fit. Unfortunately it doesn't look like any other space charge RF pentodes meeting all the criteria made it to production :(

Darryl


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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Tue 28, 2019 12:58 pm 
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Very interesting stuff! I've never seen anything like this. (been in the hobby 40 years)

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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Tue 28, 2019 1:40 pm 
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So, what's the story about this chassis? Is this something that you have?

Image

It looks like something from RCA's 1931 experimental television set that was once part of a prominent prewar RCA television collection in Noblesville, Indiana.

Image

Illustrated webpage: http://www.earlytelevision.org/rca_1932.html

Image

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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Tue 28, 2019 2:25 pm 
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That is a picture I took of the chassis from that set. I could never figure out what those contacts were for but now it makes sense.


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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Tue 28, 2019 2:45 pm 
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It makes sense for RCA to simply modify a UY base tube to accommodate an extra side pin. It was quick, cheap, and no machines had to be designed just to make a 6 pin tube base when something like this was still experimental. RCA was just a couple of years ahead of their time with these pentodes.

It sounds like you could take a 58 tube and rebase it with an extra pin, custom fitted out the side of the bakelite base, for the shield voltage. When this tube is placed in it's socket, the side pin should slide in place just fine. It may not look original but at least it would be hidden away by a tube cover.

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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Tue 28, 2019 3:11 pm 
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Michael,
That's what I original thought but now realize that won't work. The 58 is a typical pentode with the cap tied to grid 1. The P-1 has the cap tied to grid 2 and uses grid 1 as the space charge grid. It looks like only a P-1 type tube would work :(

Darryl


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 Post subject: Re: Was there ever a 2.5V Pentode with UY base?
PostPosted: May Tue 28, 2019 9:43 pm 
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I read the IRE references, and are convinced they used 24-A (224) tubes,
not 235. They were doing some groundbreaking work then. I don't think
it was realized that those tubes could operate at 60 mHz.

They did mention AVC, but the video receiver did have a manual volume
(picture volume) control. The reference was about street traffic interfering
with the transmission path causing image flutter. (We had precisely the same
effect with the first NTSC TV with " airplane" flutter years later.

The tetrode circuits would have to work well outside the dynatron kink
zones for the tubes. Had they used 235 tubes, they would mentioned what
transconductance they chose, and perhaps if it varied, how the IF response
curve would change.

As is, the paper has an error in one of the graphs, megahertz instead of kilohertz
Nothing in that setup could have worked at 400 mHz.

One thing that would be nice. IEEE could decide to dump the entire IRE
database, say from the end of vacuum tubes back, to the American Radio
Historical people. I imagine keeping it intact isn't cheap.

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