On Mon, 3 Oct 2022 13:37:33 -0700 (PDT), Ricky
<gnuarm.deletethisbit@gmail.com> wrote:

>> >You can use a big inductor after the mains bridge rectifier and before the filter cap.
>> >Some audio guys like big transformers anyways.
>> In the tube rectifier era, the pi-configuration (CLC) was common to
>> limit the rectifier current peaks. In many cases the main choke was
>> physically nearly as big as the output transformer.
>
>I think you misunderstand. In the tube era, the power filter was important to reduce the ripple feeding the circuits because they seldom used voltage regulators. Tube rectifiers were seldom other than half wave to boot!

With tubes, if you use too large cathode current, the cathode
emissivity will drop faster and the tube needs to be replaced more
often. Using too large storage capacitors directly after the rectifier
tube will degrade the lifetime of the tube.

For this reason, manufacturers specifies the maximum capacitance
allowed. typically in the 10-60 uF range. Some even allow slightly
larger capacitance if the transformer (effective) winding resistance
is large i.e. reduces the peak current.

Anyway, the voltage drop in a tube rectifier can be over 50 V with
large peak currents, which will further reduce the rectified DC
voltage, so keep the peak current reasonable. Having a relative small
first capacitor followed by an LC low pass filter then reduces the
ripple voltage.

Due to the voltage drops in mains wiring, transformer windings and the
large rectifier voltage drop, the rectified DC voltage doesn't reach
the peak voltage during the mains cycle peak, but slightly a lower
value when the mains voltage is already falling.

Ricky <gnuarm.deletethisbit@gmail.com> wrote:

> I think you misunderstand. In the tube era, the power filter was
> important to reduce the ripple feeding the circuits because they seldom
> used voltage regulators. Tube rectifiers were seldom other than half
> wave to boot!
>
> Rick C.

Most transformer-powered systems were full-wave. Here's a comparison:

Rectifier tube performance test ; 5R4 5U4 5Y3 5AR4, using 300B SE tube
amplifier

https://www.youtube.com/watch?v=ifq1Ss-HPt0

About the only half-wave rectifier tubes were the ones used in the popular
All American 5 (AA5) 5 tube radios. These ran directly off 110VAC. They
gave a nasty shock if you got the plug backwards and touched the metal
chassis and a house ground. Here's some examples:

35W4
35Y4
35Z3
35Z5

Antique radios, Old Time Radios
https://www.radiomuseum.org/tubes/tube_35w4.html
These did not handle high power. Just enough to drive a small speaker and
also give a nasty shock if you happened to touch the plate voltage and
chassis. There were so many ways to kill you in those days it's a wonder
that any of us survived.

--
MRM

On Tuesday, October 4, 2022 at 5:36:43 PM UTC-4, Mike Monett VE3BTI wrote:
> Ricky <gnuarm.del...@gmail.com> wrote:
>
> > I think you misunderstand. In the tube era, the power filter was
> > important to reduce the ripple feeding the circuits because they seldom
> > used voltage regulators. Tube rectifiers were seldom other than half
> > wave to boot!
> >
> > Rick C.
>
> Most transformer-powered systems were full-wave. Here's a comparison:
>
> Rectifier tube performance test ; 5R4 5U4 5Y3 5AR4, using 300B SE tube
> amplifier
>
> https://www.youtube.com/watch?v=ifq1Ss-HPt0
>
> About the only half-wave rectifier tubes were the ones used in the popular
> All American 5 (AA5) 5 tube radios. These ran directly off 110VAC. They
> gave a nasty shock if you got the plug backwards and touched the metal
> chassis and a house ground. Here's some examples:
>
> 35W4
> 35Y4
> 35Z3
> 35Z5
>
> Antique radios, Old Time Radios
> https://www.radiomuseum.org/tubes/tube_35w4.html
>
> These did not handle high power. Just enough to drive a small speaker and
> also give a nasty shock if you happened to touch the plate voltage and
> chassis. There were so many ways to kill you in those days it's a wonder
> that any of us survived.

The point is these 5 tube radios were the largest selling units, and half wave rectified. Many TVs that I scavenged, had single plate rectifiers with the plate cap.

Still, this is off topic from the point that the power filter was there to reduce hum, rather than anything about the input current peaks. But I suppose it served both purposes.

--

Rick C.

-++ Get 1,000 miles of free Supercharging
-++ Tesla referral code - https://ts.la/richard11209

On Tue, 4 Oct 2022 21:36:36 -0000 (UTC), Mike Monett VE3BTI
<spamme@not.com> wrote:

>Ricky <gnuarm.deletethisbit@gmail.com> wrote:
>
>> I think you misunderstand. In the tube era, the power filter was
>> important to reduce the ripple feeding the circuits because they seldom
>> used voltage regulators. Tube rectifiers were seldom other than half
>> wave to boot!
>>
>> Rick C.
>
>Most transformer-powered systems were full-wave. Here's a comparison:
>
>Rectifier tube performance test ; 5R4 5U4 5Y3 5AR4, using 300B SE tube
>amplifier
>
>https://www.youtube.com/watch?v=ifq1Ss-HPt0
>
>About the only half-wave rectifier tubes were the ones used in the popular
>All American 5 (AA5) 5 tube radios. These ran directly off 110VAC. They
>gave a nasty shock if you got the plug backwards and touched the metal
>chassis and a house ground. Here's some examples:
>
>35W4
>35Y4
>35Z3
>35Z5
>
>Antique radios, Old Time Radios
>https://www.radiomuseum.org/tubes/tube_35w4.html
>
>These did not handle high power. Just enough to drive a small speaker and
>also give a nasty shock if you happened to touch the plate voltage and
>chassis. There were so many ways to kill you in those days it's a wonder
>that any of us survived.

In the rest of the world with 220 V (or 240 V) AC (and even DC in
places, the AC/DC power supply was quite common. Radio receivers used
U-series (100 mA series heating) with a single UYnn half wave
rectifier and TVs used P -series tubes (300 mA series hearing) with
PYnn series half wave rectifier. With 220 Vac mains about 200 Vdc was
available for the electronics.

All tube TVs that I have seen had this AC/DC configuration, i.e. one
pole of the mains plug was directly connected to DC ground (and
chassis), while the other pole through the rectifier to the B+ line.
With an unpolarized mains plug meant that the chassis ground could be
directly connected to live 220 Vac.

Connecting external devices, such as audio/video recorders was quite
problematic. Audio interfacing was possible with audio isolation
transformers, but direct video interfacing became practical with
sufficiently fast optoisolators.

upsidedown@downunder.com wrote:

> In the rest of the world with 220 V (or 240 V) AC (and even DC in
> places, the AC/DC power supply was quite common. Radio receivers used
> U-series (100 mA series heating) with a single UYnn half wave
> rectifier and TVs used P -series tubes (300 mA series hearing) with
> PYnn series half wave rectifier. With 220 Vac mains about 200 Vdc was
> available for the electronics.
>
> All tube TVs that I have seen had this AC/DC configuration, i.e. one
> pole of the mains plug was directly connected to DC ground (and
> chassis), while the other pole through the rectifier to the B+ line.
> With an unpolarized mains plug meant that the chassis ground could be
> directly connected to live 220 Vac.

I was stationed in Europe with NATO just after WWII. While I was there, I
repaired many radios, notably Grundig and Telefunken. These used
transformers in the power supply and full-wave rectifiers. Also, car radios
with vibrator power supplies invariably used full-wave rectifiers.

Using AC/DC power supplies meant the filaments had to be strung in series.
This placed severe constraints in the filament warmup time, since unbalance
would lead to some tubes getting serious filament overvoltage. Also, the
number of tubes was restricted, since the total voltage had to add up to
the line voltage. This places severe constraints on the design, and I
suspect only a few manufacturers went with this approach.

Some locations used 110V for the line voltage, so manufacturers had to be
able to switch betwen 110V and 220V. This can only be done with a
transformer. These invariably used full-wave rectifiers, since half-wave is
notoriously inefficient and requires larger filter capacitors and heavier
series inductors.

I never saw any TV's while I was in Europe, but I repaired many TV's at
home before I joined the service. None of these had AC/DC power supplies.
All used transformers with full-wave rectifiers.

--
MRM

On 5.10.22 18.50, Mike Monett VE3BTI wrote:
> upsidedown@downunder.com wrote:
>
>> In the rest of the world with 220 V (or 240 V) AC (and even DC in
>> places, the AC/DC power supply was quite common. Radio receivers used
>> U-series (100 mA series heating) with a single UYnn half wave
>> rectifier and TVs used P -series tubes (300 mA series hearing) with
>> PYnn series half wave rectifier. With 220 Vac mains about 200 Vdc was
>> available for the electronics.
>>
>> All tube TVs that I have seen had this AC/DC configuration, i.e. one
>> pole of the mains plug was directly connected to DC ground (and
>> chassis), while the other pole through the rectifier to the B+ line.
>> With an unpolarized mains plug meant that the chassis ground could be
>> directly connected to live 220 Vac.
>
> I was stationed in Europe with NATO just after WWII. While I was there, I
> repaired many radios, notably Grundig and Telefunken. These used
> transformers in the power supply and full-wave rectifiers. Also, car radios
> with vibrator power supplies invariably used full-wave rectifiers.
>
> Using AC/DC power supplies meant the filaments had to be strung in series.
> This placed severe constraints in the filament warmup time, since unbalance
> would lead to some tubes getting serious filament overvoltage. Also, the
> number of tubes was restricted, since the total voltage had to add up to
> the line voltage. This places severe constraints on the design, and I
> suspect only a few manufacturers went with this approach.
>
> Some locations used 110V for the line voltage, so manufacturers had to be
> able to switch betwen 110V and 220V. This can only be done with a
> transformer. These invariably used full-wave rectifiers, since half-wave is
> notoriously inefficient and requires larger filter capacitors and heavier
> series inductors.
>
> I never saw any TV's while I was in Europe, but I repaired many TV's at
> home before I joined the service. None of these had AC/DC power supplies.
> All used transformers with full-wave rectifiers.

There were TV's with power transformers and normal 6.3V E-series tubes:
ECC88, EF89, EABC80, EL83, EL500 ...

I repaired plenty of them to enable the customers see the weekly Batman.

There is a problem with a power transformer and a picture tube, the
transformer tended to spew magnetic disturbances at the line frequency,
which was nearly the same as the frame rate, creating an undulating
picture.

--

-TV

On Wednesday, October 5, 2022 at 11:50:47 AM UTC-4, Mike Monett VE3BTI wrote:
> upsid...@downunder.com wrote:
>
> > In the rest of the world with 220 V (or 240 V) AC (and even DC in
> > places, the AC/DC power supply was quite common. Radio receivers used
> > U-series (100 mA series heating) with a single UYnn half wave
> > rectifier and TVs used P -series tubes (300 mA series hearing) with
> > PYnn series half wave rectifier. With 220 Vac mains about 200 Vdc was
> > available for the electronics.
> >
> > All tube TVs that I have seen had this AC/DC configuration, i.e. one
> > pole of the mains plug was directly connected to DC ground (and
> > chassis), while the other pole through the rectifier to the B+ line.
> > With an unpolarized mains plug meant that the chassis ground could be
> > directly connected to live 220 Vac.
> I was stationed in Europe with NATO just after WWII. While I was there, I
> repaired many radios, notably Grundig and Telefunken. These used
> transformers in the power supply and full-wave rectifiers. Also, car radios
> with vibrator power supplies invariably used full-wave rectifiers.
>
> Using AC/DC power supplies meant the filaments had to be strung in series.
> This placed severe constraints in the filament warmup time, since unbalance
> would lead to some tubes getting serious filament overvoltage. Also, the
> number of tubes was restricted, since the total voltage had to add up to
> the line voltage. This places severe constraints on the design, and I
> suspect only a few manufacturers went with this approach.

That doesn't follow. If the voltages of the tubes don't add up to the line voltage, a resistor can be added to take up the rest. It's not like tube electronics were designed for power efficiency.

--

Rick C.

+-- Get 1,000 miles of free Supercharging
+-- Tesla referral code - https://ts.la/richard11209

On Wed, 5 Oct 2022 15:50:40 -0000 (UTC), Mike Monett VE3BTI
<spamme@not.com> wrote:

>upsidedown@downunder.com wrote:
>
>> In the rest of the world with 220 V (or 240 V) AC (and even DC in
>> places, the AC/DC power supply was quite common. Radio receivers used
>> U-series (100 mA series heating) with a single UYnn half wave
>> rectifier and TVs used P -series tubes (300 mA series hearing) with
>> PYnn series half wave rectifier. With 220 Vac mains about 200 Vdc was
>> available for the electronics.
>>
>> All tube TVs that I have seen had this AC/DC configuration, i.e. one
>> pole of the mains plug was directly connected to DC ground (and
>> chassis), while the other pole through the rectifier to the B+ line.
>> With an unpolarized mains plug meant that the chassis ground could be
>> directly connected to live 220 Vac.
>
>I was stationed in Europe with NATO just after WWII. While I was there, I
>repaired many radios, notably Grundig and Telefunken. These used
>transformers in the power supply and full-wave rectifiers. Also, car radios
>with vibrator power supplies invariably used full-wave rectifiers.
>
>Using AC/DC power supplies meant the filaments had to be strung in series.
>This placed severe constraints in the filament warmup time, since unbalance
>would lead to some tubes getting serious filament overvoltage.

It took about one minute to get picture and sound.

>Also, the
>number of tubes was restricted, since the total voltage had to add up to
>the line voltage. This places severe constraints on the design, and I
>suspect only a few manufacturers went with this approach.

On P-series tubes the cathode to filament was usually specified to at
least 220 V. If the sum of the filament voltages did not reach 220 V,
just put a power resistor in series Put the actual tube filaments at
towards the cold end of the string closest to chassis ground. Thus the
filament voltage was below 220 V. Putting most hum sensitive tubes as
the last also reduced hum.

I don't know about early color TVs, did they have so many tubes that
220 V was exceeded, just put the tube filaments in two separate
strings.

>
>Some locations used 110V for the line voltage, so manufacturers had to be
>able to switch betwen 110V and 220V. This can only be done with a
>transformer. These invariably used full-wave rectifiers, since half-wave is
>notoriously inefficient and requires larger filter capacitors and heavier
>series inductors.

If you also had to support 110 Vac (and 127 Vac) you had to use a
transformer. The 127 V was used in some countries as part of the
127/2220 V three phase system

>
>I never saw any TV's while I was in Europe, but I repaired many TV's at
>home before I joined the service. None of these had AC/DC power supplies.
>All used transformers with full-wave rectifiers.

upsidedown@downunder.com wrote:

>>Using AC/DC power supplies meant the filaments had to be strung in
>>series. This placed severe constraints in the filament warmup time,
>>since unbalance would lead to some tubes getting serious filament
>>overvoltage.
>
> It took about one minute to get picture and sound.

That says nothing about overvoltage on the filaments during warmup. The
filaments on the All American 5 AC/DC tubes had an implied specification on
the filament warmup. Here is the statement:

"The 35W4 is a miniature half-wave rectifer for use in line-operated
equipment having series-connected heaters. The heater is tapped to permit
operation of a panel lamp."

https://frank.pocnet.net/sheets/093/3/35W4.pdf

Can you remember any of the rectifier tubes used in TV sets? Maybe we can
find the datasheet and see what it says about operation with series
filaments. Actually, if the filament voltage is higher than the traditional
5V or maybe 12V for later car tube radios, then we can assume it has to be
for series filaments.

[...]

>>Some locations used 110V for the line voltage, so manufacturers had to
>>be able to switch betwen 110V and 220V. This can only be done with a
>>transformer.
>
> If you also had to support 110 Vac (and 127 Vac) you had to use a
> transformer. The 127 V was used in some countries as part of the
> 127/2220 V three phase system

That is what I just said.

--
MRM

On Wed, 5 Oct 2022 22:32:34 -0000 (UTC), Mike Monett VE3BTI
<spamme@not.com> wrote:

>upsidedown@downunder.com wrote:
>
>>>Using AC/DC power supplies meant the filaments had to be strung in
>>>series. This placed severe constraints in the filament warmup time,
>>>since unbalance would lead to some tubes getting serious filament
>>>overvoltage.
>>
>> It took about one minute to get picture and sound.
>
>That says nothing about overvoltage on the filaments during warmup. The
>filaments on the All American 5 AC/DC tubes had an implied specification on
>the filament warmup. Here is the statement:
>
>"The 35W4 is a miniature half-wave rectifer for use in line-operated
>equipment having series-connected heaters. The heater is tapped to permit
>operation of a panel lamp."
>
>https://frank.pocnet.net/sheets/093/3/35W4.pdf
>
>Can you remember any of the rectifier tubes used in TV sets? Maybe we can
>find the datasheet and see what it says about operation with series
>filaments. Actually, if the filament voltage is higher than the traditional
>5V or maybe 12V for later car tube radios, then we can assume it has to be
>for series filaments.

In Europe PY8n series tubes are single rectifiers with 300 mA filament
in a Noval envelope.

IIRC PY82 (19SU, 19Y3) was often used which had 19 V filament which
indirectly heated the cathode (which is connected to the positive end
of the capacitor.

upsidedown@downunder.com wrote:

> In Europe PY8n series tubes are single rectifiers with 300 mA filament
> in a Noval envelope.
>
> IIRC PY82 (19SU, 19Y3) was often used which had 19 V filament which
> indirectly heated the cathode (which is connected to the positive end
> of the capacitor.

You have a very good memory. Congratulations.

The 19V filament definitely puts it in the series category. A typical
receiving tube in America was the 6AU6, which also has a 300mA filament.
This would allow (220 - 19) / 6.3 = 32 tubes to be run in series with the
19Y3.

The power tubes needed for audio, flyback and vertical output would also
need to have 300 mA filaments. However, the DC output of the 19Y3 is only
180mA, which is a bit on the wimpy side for a BW TV. But as an example, the
5U4, 5X4 and 5Z3 are only 225mA, so I guess it's enough. I don't know what
they would do for color sets. Maybe run two tubes in parallel.

So if the manufacturer wanted to build the absolute cheapest set with no
plans to sell it in areas with 110V, they could get away with it.

But even in Europe, there are snags. For example, in Metz, France, one side
of town was 220V and the other was 110V. So the set would have to be
switchable, which requires a transformer.

--
MRM

On Thursday, October 6, 2022 at 8:05:59 PM UTC-4, Mike Monett VE3BTI wrote:
> upsid...@downunder.com wrote:
>
> > In Europe PY8n series tubes are single rectifiers with 300 mA filament
> > in a Noval envelope.
> >
> > IIRC PY82 (19SU, 19Y3) was often used which had 19 V filament which
> > indirectly heated the cathode (which is connected to the positive end
> > of the capacitor.
> You have a very good memory. Congratulations.
>
> The 19V filament definitely puts it in the series category. A typical
> receiving tube in America was the 6AU6, which also has a 300mA filament.
> This would allow (220 - 19) / 6.3 = 32 tubes to be run in series with the
> 19Y3.
>
> The power tubes needed for audio, flyback and vertical output would also
> need to have 300 mA filaments. However, the DC output of the 19Y3 is only
> 180mA, which is a bit on the wimpy side for a BW TV. But as an example, the
> 5U4, 5X4 and 5Z3 are only 225mA, so I guess it's enough. I don't know what
> they would do for color sets. Maybe run two tubes in parallel.
>
> So if the manufacturer wanted to build the absolute cheapest set with no
> plans to sell it in areas with 110V, they could get away with it.
>
> But even in Europe, there are snags. For example, in Metz, France, one side
> of town was 220V and the other was 110V. So the set would have to be
> switchable, which requires a transformer.

I don't follow that. Why couldn't they wire the tubes in two strings for 110V? A simple switch could make the selection. That's how they switched the transformer between the two voltages, two primary coils, either in series or in parallel. Same with tube filaments. I would expect it was more the plate voltage that would be hard to design to work with either 110V or 220V.

--

Rick C.

+-+ Get 1,000 miles of free Supercharging
+-+ Tesla referral code - https://ts.la/richard11209

On Fri, 7 Oct 2022 00:05:51 -0000 (UTC), Mike Monett VE3BTI
<spamme@not.com> wrote:

<About PY82 and other rectifier tubes

>The power tubes needed for audio, flyback and vertical output would also
>need to have 300 mA filaments. However, the DC output of the 19Y3 is only
>180mA, which is a bit on the wimpy side for a BW TV. But as an example, the
>5U4, 5X4 and 5Z3 are only 225mA, so I guess it's enough. I don't know what
>they would do for color sets. Maybe run two tubes in parallel.

It should be noted that color TV service (PAL/SECAM) started in Europe
in the 1960's, so solid state rectifiers were available.

On Friday, 7 October 2022 at 04:35:53 UTC-7, upsid...@downunder.com wrote:
> On Fri, 7 Oct 2022 00:05:51 -0000 (UTC), Mike Monett VE3BTI
> <spa...@not.com> wrote:
>
> <About PY82 and other rectifier tubes
> >The power tubes needed for audio, flyback and vertical output would also
> >need to have 300 mA filaments. However, the DC output of the 19Y3 is only
> >180mA, which is a bit on the wimpy side for a BW TV. But as an example, the
> >5U4, 5X4 and 5Z3 are only 225mA, so I guess it's enough. I don't know what
> >they would do for color sets. Maybe run two tubes in parallel.
> It should be noted that color TV service (PAL/SECAM) started in Europe
> in the 1960's, so solid state rectifiers were available.

Even with monochrome sets in the UK most were using selenium HV rectifiers by the late 50's. Valve rectifiers weren't common.

I never saw any radios in the UK with transformerless power supplies - they all used mains transformers.

I suspect one of the reasons why the US type of transformerless design never took hold is that with only ~5 valves the total heater voltage would be nowhere near 240V and so would require a lot of power being dissipated in the heater dropper resistor.

There were 100mA heater valves available such as the UL84. I only seem to remember seeing them in record players where the heaters ran off a tap on the motor winding with a selenium rectifier for HT. There would only be one or two valves in the amplifier fed from a low-quality crystal pick-up with couple of volts output.

There may have been radios using them but they didn't seem to be common.

kw

upsidedown@downunder.com wrote:

> On Fri, 7 Oct 2022 00:05:51 -0000 (UTC), Mike Monett VE3BTI
> <spamme@not.com> wrote:
>
> <About PY82 and other rectifier tubes
>
>>The power tubes needed for audio, flyback and vertical output would also
>>need to have 300 mA filaments. However, the DC output of the 19Y3 is
>>only 180mA, which is a bit on the wimpy side for a BW TV. But as an
>>example, the 5U4, 5X4 and 5Z3 are only 225mA, so I guess it's enough. I
>>don't know what they would do for color sets. Maybe run two tubes in
>>parallel.
>
> It should be noted that color TV service (PAL/SECAM) started in Europe
> in the 1960's, so solid state rectifiers were available.

Great. So how did they handle the filaments and the filament to cathode
voltage? Or did they just go to transformers?

--
MRM

On Friday, 7 October 2022 at 11:47:54 UTC-7, Mike Monett VE3BTI wrote:
....
> > It should be noted that color TV service (PAL/SECAM) started in Europe
> > in the 1960's, so solid state rectifiers were available.
> Great. So how did they handle the filaments and the filament to cathode
> voltage? Or did they just go to transformers?
>
The valves had to be designed with appropriate heat to cathode voltage limits.

Some signal valves such as EF80 only tolerated ~150v (http://www.r-type.org/pdfs/ef80.pdf) so would have to be lower on the heater chain.

Others such as the line-output devices (PL81, PY81 and PL36) could tolerate higher voltages (>200V) and could be higher up.

http://www.r-type.org/pdfs/pl81.pdf
http://www.r-type.org/pdfs/py81.pdf
http://www.r-type.org/pdfs/pl36.pdf

kw

On Fri, 7 Oct 2022 10:56:38 -0700 (PDT), "ke...@kjwdesigns.com"
<keith@kjwdesigns.com> wrote:

>I suspect one of the reasons why the US type of transformerless design never took hold is that with only ~5 valves the total heater voltage would be nowhere near 240V and so would require a lot of power being dissipated in the heater dropper resistor.

I once had an AC/DC LW/MW/SW receiver using U-series (100 mA) tubes
(two UCH21, UL21 and UY1N). The filament voltage was 20 + 20 + ´45 +
50 = 135 V. add to this two 18 V dial lamps and the total
voltage drop was 161 V. The resistor only had to dissipate 59 V (6W).

The receiver had been originally used in an apartment building owned
by a tram company, which even in the 1950's used 220 Vdc.

upsidedown@downunder.com wrote:

> I once had an AC/DC LW/MW/SW receiver using U-series (100 mA) tubes
> (two UCH21, UL21 and UY1N). The filament voltage was 20 + 20 + �45 +
> 50 = 135 V. add to this two 18 V dial lamps and the total
> voltage drop was 161 V. The resistor only had to dissipate 59 V (6W).

Nice.

UCH21 X2
Vf 20 Volts / If 0.1 Ampere
Tube UCH21; Triode-Heptode
https://www.radiomuseum.org/tubes/tube_uch21.html
- why two?

UL21 Vf 45 Volts / If 0.1
Tube UL21; Vacuum Power Pentode
https://www.radiomuseum.org/tubes/tube_ul21.html

UY1N Vf 50 Volts / If 0.1
Tube UY1N; Half-Wave Vacuum Rectif
https://www.radiomuseum.org/tubes/tube_uy1n.html

See also List of Mullard�Philips vacuum tubes
https://en.wikipedia.org/wiki/List_of_Mullard%E2%80%93Philips_vacuum_tubes

--
MRM