How bad does it have to be before its a scrapper set?

[Mike Watterson]

The speaker is missing too. But I have a few old larger speakers.
https://www.radiomuseum.org/r/pye_t19dt_19.html
I was toying with the idea of adapting it to use Russian Rod Pentodes. Seeing if it would "go" simply changing LT.
ECH35 can be replaced by two, one as a pentode mixer and one as triodised pentode oscillator (also works in a heptode or octode socket).
EF39 easily replaced by 1j29b. The 1j24b maybe a lot less gain.
EBC33: Triodised 1j24b and 1N60.
EL33: 1p24b or 1j29b depending how loud you want. Or change to push-pull for about x3 power and then a mains 110 -110 transformer is good for audio.

AGC is an issue. The only way to do it is varying g2 on the amps, not g1 (25V almost no gain, 50V loads of gain) as they are inherently sharp cutoff. That would need an AGC amp.
However the LO coils/Osc will work, RF coils too. The IFTs will work, as I've tested the Rod Pentodes in a couple of unmodified battery valve sets.

The hardest things doing a multiband radio from scratch are the RF, LO and mechanics of tuning scale. IF and Audio are no bother. Layout and switching of RF & LO gets hard beyond two or three bands.

Or I can do Octal. No EL33s, but KT61 and 6V6 are available.

[boater sam]

Rod pentode route is very ambitious, I have no experience with them.
 KT61 output/s would be good, 6V6 or 6BW6 easy too.

Are you taking the challenge?
Sam.

[Mike Watterson]

I'll do something. Likely get RF to detector (with an 1N60) working with ECH35 and EF39, then decide what to do next.
The coils and IFTs on mains sets are similar to battery models (valves).
The big difference is LT and bias. No self bias with cathode resistors. So short them all out and provide -Ve bias via grids, or run filaments -ve vs 0V. Mains /battery sets use series filaments to set grid bias, hence O/P last and audio preamp with grid leak is first. Parallel sets used to use a grid bias battery, lasts for shelf life, then used HT- current to get -Ve bias.

The only harder bit than say using 2V or 1.4V octal battery valves is the sockets. The only tricky bit on Rod Pentodes is AGC as they are sharp cutoff. One could just have a variable voltage to g2 for manual RF gain (done on some battery communication receivers).

Obviously HT wants to be 45V to 120V depending on location. I also have a Philips VHF tuner head for 2x EF80s. That will easily work with Rod Pentodes with suitable adaptation. Cathode feed is done by feeding filament via bifilar RF choke, the DC cancels and it's high impedance to the RF.

Even if I repopulate with original valves I may add the Philips EF80 tuner head. I doubt it tunes past 101MHz!

[boater sam]

Even if I repopulate with original valves I may add the Philips EF80 tuner head. I doubt it tunes past 101MHz!

Use one of the redundant shortwave bands?
Can these be adapted easily to go up to 108 MHz?
Sam.

[Mike Watterson]

Use one of the redundant shortwave bands?
Can these be adapted easily to go up to 108 MHz?
Sam.

I doubt it. EF80 struggles to do 101MHz. It might do better with Rod Pentodes. Almost any other valve ever used for VHF is better than the EF80. ECC85, ECF82. USA used nuvistors at the end. They used up to 108 in 1945, not sure what valves. Philips seems to have persisted with EF80s for UK market when they already obsolete for VHF.

I'd fit an AM/FM switch. Don't forget the VHF head needs an IF amp with more stages and an FM detector of some kind.
Schaub-Lorenz (ITT) had some battery valve sets that saved a DF97 and used cheaper DF96 IF amps. It used the DK96 as a fixed frequency changer with 10.7MHz IF in and 6.5MHz IF out. The DK96 and DF96 then had 6.5MHz double tuned IFTs in series with the AM IFTs (460KHz?). Then a pair of germanium diodes as discriminator, as all battery valve FM sets had used since 1953. The DC90 as a self oscillating mixer enabled VHF on battery sets in 1953. The aerial circuit needed carefully aligned to avoid LO radiation. I think the 1st valve on most mains VHF head is more to limit LO radiation (harmonic would affect band III TV), especially the EF80, which is a buffer, not really any gain.
I've checked and a DF97 works in a DF90 socket, and vice versa, no noticeable shift in tuning. It's triodised.
The Vidor Vanguard is unusual apart from being one of only two UK VHF valve portables (The Sky Monarch II, or AM/FM, is battery, but a table model for people with no mains) and the first in the UK 1957 (four years after most of Europe). Unlike all the continental AM/FM valve sets it has no DK96 or DK92 etc. The Triodised DF97 which is VHF self oscillating mixer (like most AM transistor LO/mixer), is also the MW & LW local oscillator. The 1st 10.7MHz IF is then a Pentode mixer for AM. So it's all DF97s apart from the DAF96 and DL96. Also unusually no telescopic rod. The "piping" hiding the seam on the cloth cover is the VHF loop.
It works far better than the Sky Emperor and nearly as well as the Philips Annette on VHF, with advantage of no aerial rods. The aerials on the Sky Emperor are horrid.

[boater sam]

Use one of the redundant shortwave bands?
Can these be adapted easily to go up to 108 MHz?
Sam.

I doubt it. EF80 struggles to do 101MHz. It might do better with Rod Pentodes. Almost any other valve ever used for VHF is better than the EF80. ECC85, ECF82. USA used nuvistors at the  end. They used up to 108 in 1945, not sure what valves. Philips seems to have persisted with EF80s for UK market when they already obsolete for VHF.

I'd fit an AM/FM switch. Don't forget the VHF head needs an IF amp with more stages and an FM detector of some kind.
Schaub-Lorenz (ITT) had some battery valve sets that saved a DF97 and used cheaper DF96 IF amps. It used the DK96 as a fixed frequency changer with 10.7MHz IF in and 6.5MHz IF out. The DK96 and DF96 then had 6.5MHz double tuned IFTs in series with the AM IFTs (460KHz?). Then a pair of germanium diodes as discriminator, as all battery valve FM sets had used since 1953. The DC90 as a self oscillating mixer enabled VHF on battery sets in 1953. The aerial circuit needed carefully aligned to avoid LO radiation. I think the 1st valve on most mains VHF head is more to limit LO radiation (harmonic would affect band III TV), especially the EF80, which is a buffer, not really any gain.
I've checked and a DF97 works in a DF90 socket, and vice versa, no noticeable shift in tuning. It's triodised.
The Vidor Vanguard is unusual apart from being one of only two UK VHF valve portables (The Sky Monarch II, or AM/FM, is battery, but a table model for people with no mains) and the first in the UK 1957 (four years after most of Europe). Unlike all the continental AM/FM valve sets it has no DK96 or DK92 etc. The Triodised DF97 which is VHF self oscillating mixer (like most AM transistor LO/mixer), is also the MW & LW local oscillator. The 1st 10.7MHz IF is then a Pentode mixer for AM. So it's all DF97s apart from the DAF96 and DL96. Also unusually no telescopic rod. The "piping" hiding the seam on the cloth cover is the VHF loop.
It works far better than the Sky Emperor and nearly as well as the Philips Annette on VHF, with advantage of no aerial rods. The aerials on the Sky Emperor are horrid.

Very interesting, thanks Mike. Vidor Vanguard is new to me, didn't realise it is a bit of an unusual set.
Any advantage in using the EF184 instead of EF80? I see Mullard quoted the performance of both at 40 MHz but if EF80 is good for 100 MHz will the EF184 exceed this? I thing the possible gain is better too.
Sam.

[Mike Watterson]

I've no idea about the EF184 (1958 or 1960?). It does seem pin compatible and a later version. I've never seen it used.
Or indeed the EF89 (replaces EF85, the variable mu version of EF80?). The two cathode pins become cathode and screen. Likely a problem.
Certainly if I get the VHF working with the EF80 I can look.
I have a spectrum analyser, wobbulator (455K and 10.7M), various analogue signal generators, a DDS generator, uTracer. So I can investigate.
I'm tempted to add 470kHz, 6..0 6.5 and maybe 39MHz to the Wobbulator as well as a external fixed Fin marker.
The cheap 0.1MHz step 87MHz to 108MHz stereo FM modulators for MP3 to car radio are handy too.

[boater sam]

EF183 replaces EF85, variable mu.

[Mike Watterson]

Never seen EF183 in anything. Though my memory of valve TVs in 1970s is as bright as most EM34s. Have seen loads of EF89s

[pwdrive]

EF183/184 were primarily TV valves.

Lawrence.