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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 7th Feb 2019, 5:32 am   #21
Synchrodyne
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Default Re: 12AH8 - battery valve substitute?

Here are the scans of those Mullard aticles.

Cheers,
Attached Files
File Type: pdf Mullard TC 25 Hybrid Car Radio.pdf (520.2 KB, 57 views)
File Type: pdf Mullard TC 29 MW & SW Hybrid Car Radio.pdf (332.5 KB, 66 views)
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Old 7th Feb 2019, 11:09 am   #22
Synchrodyne
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Default Re: 12AH8 - battery valve substitute?

The Mullard TC 25 article as posted was missing a couple of pages. Here is the complete version.


Cheers,
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File Type: pdf Mullard TC 25 Hybrid Car Radio.pdf (682.9 KB, 63 views)
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Old 7th Feb 2019, 7:14 pm   #23
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Default Re: 12AH8 - battery valve substitute?

Synchrodyne

Thank you for uploading those excellent scans,a very detailed analysis of the valve applications, parameters and circuit optimalising.
Had been searching for a copy of that manual for years,either to buy in its published form or as a download.

Much appreciated

Mike

Last edited by VT FUSE; 7th Feb 2019 at 7:30 pm.
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Old 7th Feb 2019, 10:19 pm   #24
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Default Re: 12AH8 - battery valve substitute?

Quote:
Originally Posted by Synchrodyne View Post
Here are the scans of those Mullard aticles.

Cheers,
Great articles, I wish I had prior to building my EF-98/OC16 radio. I found out the hard way about the ECH83's triode not being suited to SW use. Also, about the gain differences in MW vs SW. I solved the problem differently by adding another IF stage and modifying the audio gain with a transistor switch in MW vs SW modes. I could have switched one EF98 to an ECH 83 to get an extra triode for the audio, and added another EF98 for the VFO, but the MPF102 makes such a great VFO and by adding another as a buffer I could also get a low Z out for a frequency counter (that has an IF offset), so I did that instead.

The circuit I posted also shows the other oddball thing about the radio, I used a miniature industrial Telemechanique switch (for the SW-MW band change) because they look and feel so good and practically never wear out, totally unsuited to RF switching because of that, but used it to switch sealed Teledyne relays to actually do the RF switching. These have a habit of staying good & reliable over time and of course never need cleaning, unlike the usual rotary band change switch.
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Old 15th Feb 2019, 1:45 pm   #25
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Default Re: 12AH8 - battery valve substitute?

Thank you Synchrodine for those uploads, they look really interesting.

Hi again Mike and Hugo, great contributions , thank you.

I’ve done a little audit of valves that I’m curious to use. Not only do I have the ECH83, but also little doorknob types 7171A (US military) and Mullard DK91 (battery heptode), as well as two acorn types RCA955.

Not necessarily all at once: I may make a UHF oscillator /mixer just to see how high I can go with the little doorknob types, I may o the other hand start with a VHF receiver.

I know I could make a VHF front end with the acorns... I’m not sure what the upper limit is for the battery heptode as an oscillator?

I know the RCA955 acorn on the other hand ,was used at 144Mhz during the Second World War (as a test oscillator on board Blenheim aircraft)

Are there grounded grid circuits for eg ECH83 , equivalent of the familiar MPF102 grounded gate cct?

ECH83 still attractive if good to VHF.

I’ve sorted the audio stage which will be using vintage transistors including Ge types.

A time for mulling, really open to ideas . I’m aware that the original direction of this thread was low anode HT, so of course I’m happy to stay on track with that.
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Old 15th Feb 2019, 5:08 pm   #26
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Default Re: 12AH8 - battery valve substitute?

The Acorns would happily go up to 400MHz; they were widely used in both UK and US WWII military gear - both 'designed-for-the-Military' stuff and civilian/commercial gear co-opted into military service like the Hallicrafters S27 and successors.

They also work down to surprisingly-low voltages (I remember a battery-heater Acorn-based GDO that used a 22.5V hearing-aid battery for HT).

They did seem to have a short period in the spotlight in the 1930s but by early-WWII they had become deprecated and B7G valves took over (some early versions of which were really Acorn electrode-assemblies fitted to a B7G base).
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Old 15th Feb 2019, 5:38 pm   #27
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Default Re: 12AH8 - battery valve substitute?

That’s good to know about Acorns. I might experiment at UHF+, in that case! Thank
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Old 15th Feb 2019, 6:01 pm   #28
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Default Re: 12AH8 - battery valve substitute?

The first US-made post-Acorn B7G valves were the 9001/9002/9003: like I said, the same basic Acorn electrode assembly in a B7G bottle.

The 717A Octal "Doorknob" in turn got B7G-ized as the 6AK5.

Somewhere I've got a late-1930s US schematic for a 2-valve 430MHz "Walkie-talkie" type transceiver that uses an Acorn triode as a superregen detector on receive and as a self-excited oscillator on transmit; the other valve is the receiver audio-amp which then gets switched to modulate the oscillator on transmit.

The same idea reappeared a bit later on:

http://www.rfcafe.com/references/qst...r-1945-qst.htm

though I doubt the FCC/CAA would be impressed with anyone operating such a device in the civilan airband these days!
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Old 15th Feb 2019, 8:27 pm   #29
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Default Re: 12AH8 - battery valve substitute?

Al

If considering lowish Anode Voltage and grounded grid designs,the frame grid pcc89 double Triode,which was optimised for grounded grid application will operate superbly at 36V HT or so in experimental circuits,the heater may or may not be awkward to feed as it is 7.5V 300mA for series string tv use,maybe a dropping resistor or 6.3V transformer feeding a bridge rectifier and around 25uF reservoir cap will give a little over 7V dc-you will need to play about with the cap value.
The full HT was intended to be only 90V in tv tuner usage.I have run new ones with good emission at 12V HT and they performed well.
For optimal 12V operation the ecc86 takes some beating in vhf front ends such as you envisage.

Mike

ps-an interesting thread,keep us informed please.
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Old 15th Feb 2019, 10:33 pm   #30
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Default Re: 12AH8 - battery valve substitute?

Quote:
Originally Posted by astral highway View Post
ECH83 still attractive if good to VHF.
Not so likely, I suspect. The ECH81 itself was specified to work up to 100 MHz. It was envisaged that the triode section could be used as an FM mixer-oscillator, usually preceded by a suitable RF amplifier, and with the heptode section used as the 1st FM IF amplifier.

Given that the ECH83 triode fails as an oscillator for the upper HF band, it probably is not going to do too well at 100 MHz. It might though be usable as an FM mixer with an external oscillator. Whether the EF98 – used as an external oscillator for the Mullard SW car radio circuit - would reliably oscillate at around 100 MHz is unknown.

Quote:
Originally Posted by astral highway View Post
Are there grounded grid circuits for eg ECH83 , equivalent of the familiar MPF102 grounded gate cct?
Given that the ECH81 triode could function as an FM mixer-oscillator, one might expect that it could also have been used as an FM RF amplifier. If so, then considered in isolation, it could have been used in either grounded cathode or grounded grid mode (or a combination of both). But the fact that the triode and heptode shared a common cathode pinout effectively limited its use to the grounded cathode mode only, so that the heptode cathode could be at RF ground. For that reason I should not expect to find grounded grid circuits for any of the triode hexode/heptode types, given that the common cathode was an almost universal feature. Also, many (although not the ECH81, ECH83, ECH84 and 20D4) had the triode grid internally coupled to the hexode/heptode grid 3, which further limited their non-mainstream utility.

And that prompts a look over into left-field where one may spy the ECH200. This did have separate cathode pinouts for the triode and heptode sections. It was the successor to the ECH84, intended for use as a noise-gated sync separator in TV receivers. Recall that the ECH84 was designed specifically for this purpose, and superseded the ECH83 and ECH81 that had previously been pressed into this service. The ECH200 heptode section at least was designed to operate with very low anode voltages. I don’t know how the triode section would work with very low HT, or even how well it would function at VHF with normal HT. But if want to see what can be done with triode heptodes per se, it might be worth a look. Note that the heptode is of the sharp cutoff, short grid-base type, not of the remote cutoff type normally used in radio work. But that said, one can find examples where the 6BY6 and 6CS6 (EH90) were used as mixers or self-oscillating mixers in HF receivers. Both were sharp cutoff, short grid-base heptodes developed for use as noise-gated TV sync separators after Zenith had shown the way by pressing the 6BE6 radio valve into this service.

Re the PCC89 cascode valve, there were also normal 6.3-volt versions, namely the ECC89 and ECC189. The latter was used in several HF receivers, including late Eddystone models, so is likely to be commonplace. The ECC88 was the sharp cutoff counterpart, and may also be a candidate.


Cheers,
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Old 15th Feb 2019, 11:15 pm   #31
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Default Re: 12AH8 - battery valve substitute?

The 6.3V ecc89 and ecc189 are quite becoming scarce and I keep my spares for communications receivers such as my two Eddystones.
The country is awash with pcc89 and pcc189's, examples of which I have in my stocks and which are frequently seen on auction sites at low prices.
The thinking behind suggesting the 300mA versions is that for experimental use they can really be treated as consumables.
The audio market has pushed ecc88 prices skyward and many examples offered secondhand turn out to be pulls from oscilloscopes,tired from use and have low emission or are noisy in receivers hence the reason that sensibly priced and abundant substitutes may be a consideration.

Mike

Last edited by VT FUSE; 15th Feb 2019 at 11:24 pm. Reason: small addition
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Old 19th Feb 2019, 1:55 am   #32
Al (astral highway)
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Default Re: 12AH8 - battery valve substitute?

Hello all,

I'm just checking in to acknowledge your detailed posts and to thank all of you. There's a lot to think about here and several directions to pursue.

I'll make more specific replies later in the week when I've had a think. Mike, I'll definitely keep you updated as a direction begins to form.

Cheers!
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Old 19th Feb 2019, 2:41 am   #33
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Default Re: 12AH8 - battery valve substitute?

Al,

Remember this thread:

https://www.vintage-radio.net/forum/...d.php?t=141192

Don't forget about the 6CW4.

(I still think that cool looking guy with the giant walkie talky looks like one of the Righteous Brothers).
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