Michael Watterson

HMV 2007R transportable record player

 Restorations  Comments Off on HMV 2007R transportable record player
Aug 132020
 
Open HMV 2007R transportable record player

HMV 2007R transportable record player

I was surprised to see this in the local animal welfare charity shop. I thought it looked too large to be an attaché case radio and too small to be a record player. Though it was styled like many 1950s UK attaché case radio models.

Opening it revealed it was a record player. I was also surprised at the lack of hits online doing a search. The most similar model is the HMV RE.11.AM which might have replaced it. It’s not on the Trader Sheets or R&TVS. The 2006 and 2008 are listed in R&TVS, but though they are record players, they are later. The 2006 seems later and more advanced than the 2008 as it’s an optionally stereo, transistor model.

The wires had been pulled off the pickup. The stylus arms were bent around the tip of the cartridge. Connecting the ‘scope revealed that the cartridge is working, so I removed it, pulled off connectors, cleaned the green corrosion of the pins and straightened the strips holding the styli. I re-soldered the cable to the clips with them still off the cartridge as soldering heat can damage it. The arm tracking weight spring was in the end hole of the retaining strip, so I moved it midway for now as that would have been greatest loading.

The dual 32 + 32 µF capacitor tested fine for leakage at 32V and discharged slowly on the PSU meter. The 3.3 kΩ main dropper resistor was fine.

The 100uF 10V two piece plastic case Plessey capacitor on the cathode resistor was dried out and replaced with a 35V 106 °C 100uF part. There was also a 0.1 µF paper dielectric capacitor on the screen grid to chassis with an associated 4.7 kΩ series resistor to HT. It was leaky and replaced with a 630V polyester type. The chassis end of both original capacitors was left connected.  The selenium rectifier was left in place and a 4 way screw terminal block used its pins to mount a 1N4007. No additional series resistance is needed in this design.

The 1nF 1 kV paper dielectric capacitor between the electrical chassis, which could be either side of the mains, and the main turntable base was snipped where it connected to the chassis end of the volume control. This didn’t have R3, 1.5 MΩ, but did have a simple loudness feature implemented by a 220 pF silver mica capacitor between input and output.

Powered on. Nothing, not even hum. The HT was OK and the UL84 heater was glowing. A known good one was substituted, but there was no change.

The nut driver is needed to take out the two retaining nuts. Examination revealed that the cathode and grid pins where bent and soldered together!  Strange. The solder was removed and pins bent apart. The input screened cable then needed reconnecting to the grid pin. There is no grid leak resistor or series capacitor no doubt to save two parts and the bias is set by the cathode resistor.

Now it badly played the 78. The volume control was strange. Fixed by spraying in some WD40 at the terminals, it dries to leave a thin wax film, which is why it’s a bad lubricant. The speed issue and noise from the platter was due to the idler being totally perished.

I tried supergluing a synthetic O ring around it as the actual diameter isn’t critical. But it made it too fat. Then I remembered I’d dismembered a cheap scrap Currys reel to reel taperecorder at the same time as restoring two others. Could one of its idler wheels fit?

It was like in new condition despite the heads on that machine being badly worn away. The thickness seemed OK as did the diameter. Perhaps a shade thicker, but the poor condition made it hard to tell.
The original had two metal shim washers and a fibre washer under it. Moving the fibre washer to the top made the edge match the speed steps on the motor shaft. The internal diameter and boss height was the same!

Now it played 33, 45 and 78 perfectly and the noise was gone from the platter. No doubt the two styli are sapphire and worn, but it depends how much it was used.

It’s not very loud, but I don’t know if it’s due to having only a single UL84, a worn out cartridge or the 160V HT. There is no voltage adjustment. Our mains is typically about 230V here in Ireland, but most English people I know seem to have a little more than 240V. The other UL84 is loud in the radio and is not actually as loud in the record player. However it sounds quite good for such a simple turntable and amplifier.

Herge-2

 Russian Rod Pentode, Valve project  Comments Off on Herge-2
Apr 042018
 

The finalised design has a generous gain Audio Amplifier that can even drive a loudspeaker via a transformer and actually needs a volume control on stronger stations!

A loop aerial
The finished Hergé radio (with reaction for volume)

 

The theory is that using a loop aerial as the tuning coil (with a feedback coil on it too) will remove the need for a separate aerial and earth. Also less local electrical noise will be received compare with a whip or long wire aerial.

The aerial loop / tuning coil has 5 coils wound side by side. When you put 2 x 0.6mH inductors in series you get 1.2mH, put them in parallel you get 0.3mH. But if they are very close the two inductors become ONE inductor with twice the turns. Inductance of a simple coil is proportional to N2 so you get 2.4mH if two coils wound with each strand side by side are in series. If they are in parallel you get the same inductance, but it’s as if you used fatter wire or “Litz” wire, the “Q” is increased. In this case I have 4 coils for tuning and the 5th is the feedback or tickler coil. Putting four in series should be 2.4mH, fine for LW. two pairs in parallel/Series is 0.6mH, fine for MW. All four in parallel is maybe 0.3mH, and should do about 1.7MHz to 4MHz. Or 3.5MHz to 6MHz if you have a smaller tuning capacitor.

 

Note the first coil is wound with about 4.5mm spacing and each subsequent coil has each turn beside the previous, with about 0.8mm to 1mm pitch (about 0.9mm average). Each coil is about 16 turns (the number of turns depends on the overall arm size, the prototype loop is 41cm tall and 41cm wide using about 7.6cm width of a 9cm wide baton ).

The circuit concept dates from the 1920s! Only a 1.5V AA cell for “filament” (LT = Low Tension) and a few PP3 batteries for HT (High tension).

With an external amplifier it will work with just 2 x PP3 batteries (16V to 19V HT). With a “crystal earpiece” very like those in the 1940s to 1960s (available today in Maplin for €3) and 27V to 90V HT it is audible with no extra amplifier. You’d need a strong station and good ears for 27V (3 x PP3) but it’s quite good at 6 x PP3 (about 45 to 50V). At 8 x Alkaline PP3s it’s quite loud!

With suitable C13, C14 and coils it will work on LW, MW or SW.

How  it works

With a Pentode rather than Triode operation the advantage is that you don’t need an RFC (Radio Frequency choke) on the Anode. The screen grid is essentially acting as a psuedo RF Anode and the actual anode as AF Anode.

Regeneration is essentially “Q” multiplication by using the screen grid for controlled positive feed back to cancel the losses of the coil (which lowers Q). The Q becomes very high just before oscillation. The Pentode characteristics are such that the valve is also a mixer, so at almost oscillation the carrier mixes and creates baseband and twice frequency components (What people called Homodyne/Syncrodyne, though these are regarded as two diffferent modes by some writers). Since the Anode is decoupled at RF (220K and 470pF), only the modulation is left on the anode.

I can only test MW at night as there are no MW stations near. But Five Live and “Absolute Radio” 1215 very clear from Twilight.

R1 RTE 252 LW during day with very faint BBC R4 and slight “growls” on other LW frequencies.

Anyway, no diode detector needed.

Normally there is a series resistor bypassed with capacitor to bias the grid more negative. At the 18V to 22V HT (PP3s sitting on the filament supply) and grid biased to 0.25V below “f-” (the 12 Ohm resistor between -LT and f-) the bias is OK. Adding such a “grid leak” scheme makes it tend to oscillate at low audio frequencies.

Also there are usually a couple of RFCs (Radio frequency chokes) with problems of self resonance. The “reaction” or “tickler” coil feedback is often adjusted with a variable capacitor for historic reasons, now a 50K Ohm pot is much easier to get. A 100K may be a little better.

The Aerial is often coupled via a 3rd winding. If the aerial is very long or 50 Ohms, then a 3rd winding with about 1/3 or 1/4 the number of turns of the “tickler” or feedback winding may be needed. A Short whip is very high impedance and the series coil helps match it and reduce its tendency to affect the tuning. I used a “resistor” sized 1mH coil. You can wind an air core one.

Next to try is a tuned loop so no separate aerial whip is needed. It will have two windings and replace the coils. If the main winding is two parallel windings of 35 turns on about 18″ (45cm), I think switching from parallel to series will quadruple the inductance an thus the one loop will work for LW & MW.

The colours are the “standard” large ferrite rod aerial colours. If winding your own make the “tickler” or feedback coil about 1/4 turns of main coil and beside it on ferrite, or on top at “earthy end” on air-cored. If there is silence at all positions of pot, reverse connections on the feedback winding. It should get noisier as pot slider moved from HT resistor. If near a station it will squeal if turned to high. If turned full it will be totally silent again as the circuit simply oscillating. So adjust pot over full travel before deciding the feedback wires need reversed.

1.0V to 1.35V is fine on the filament. These are not like D-series battery valves, which are designed for direct connection to Carbon-Zinc, these are designed for NiCd batteries. Hence 0.9V to 1.4V limits in data sheet. The extra 0.25V across filament resistor really optimises the grid bias at these low HT volts.

 

Battery valves historically used nominal 22.5V, 45V, 67.5V and 90V HT packs and sometimes 6 x 1.5V “D” size Zinc Carbon cells in parallel for “LT”. Performance was best with 90V. The 22.5V was very poor and only used in hearing aids.  Some packs combined the LT & HT in one box. Though the batteries where expensive, they lasted much longer than a modern DAB Radio. The large cabinets (often wood) and 6″ to 8″ loudspeakers meant that late model Battery portables sounded far better than the early 1960s transistor radios that killed them off.

 

Specification

Approximately 170KHz to 270KHz on LW and 550KHz to 1200MHz on MW.

4 x AA Alkaline nominal6V LT @ 21.5mA  (about 120 hours), 4 x C cells would be better match to HT life

4 x PP3 Alkaline nominal 36V HT @ 700uA  (about 250 hours)

4 x 1j18b valves. (Cost under 3 Euro total excluding postage)

No external aerial or earth required.

 

 

Warning!

Note that higher voltages are dangerous, especially above 50V. There is also risk of fire and burns or even explosions if NiMH are used to make higher voltage packs.

Comparison

The latter half 1950s Battery portable radio sets used a loop aerial in the lid. They used 125mA LT 1.5V and about 6.5mA HT from 90V pack. Line up DK96, DF96, DAF96 and DL96. Usually LW & MW.  The earlier 1950s and late 1940s miniature valve sets used DF91 which is twice the filament current. They had more variation of valves and design and up to 250mA LT 1.5V current.

The “Hergé” uses 24mA from 4 x AA cells (6V) and about 1mA from  4 x PP3 (36V)

The chassis is a piece of plywood (Hardboard or MDF will do too) mounted on battens deep enough to house PP3 battery. If you want C or D cell instead of AA cells for the “filament” supply (LT = Low Tension), then use taller battens.

Loop Aerial on empty chassis

My base is 26 x 17cm, but a bit wider would be fine.

The front panel is easiest to do neat if 2mm plastic sheet. But Aluminium or MDF can be used. Perspex / Acrylic is difficult to work without cracks. A disk type motorised tile cutter will cut Perspex or thin Aluminium sheets. My front panel is 12cm x 26cm x 2mm.

The coil / aerial  is supported on two bits of panelling wood 41cm x 8cm x 9mm with the tongue and groove split off. This makes the coil “diameter” vary from 30cm to 42cm

The “cross” is supported a few cm above the base by a 3rd piece of panel board.

The 3 x 1.5V AA cell (with two dummy cells if only one valve) and the 4 x PP3 batteries are mounted on a plastic or wooden board screwed to the bottom. (was 8, but four is fine)

The valve is mounted on screw terminal block, though you can use veroboard/stripboard.

mount the 1j18b pentode valve

You can see the slow motion drive variable capacitor mounted to base. The front panel is scored with a line at height of centre of the shaft. A small screw driver blade was poked through and the hole enlarged by twisting a scissor blade till it was required size. You can use a vertical drill. Then the other controls and socket mounted at same height.

mount the regen. feedback pot

For convenience of re-wiring and for those inexperienced in soldering you can cut the excess plastic off sides and one end of screw terminals and fit them on the Pot and Tuning capacitor.

You can see the PP3 batteries only need one clip, cut in half:

The battery pack

The next page in the series will discuss the circuit revisions and design of the coil.

The radio is working on MW and LW, though in Limerick MW only at night.

It’s a bit faint, and WWII versions such as “sweetheart” that used an external aerial (more signal) used three valves. So there is an addon amplifier option.

The complete Hergé

Side view

The complete Hergé (side)

A four pole two way toggle switch is mounted on the “aerial frame”. The main tuning coil is two coils wound in parallel, that are wired in parallel (more Q) for MW and in series for LW (x4 Inductance). The green wire at the edge is 5 turns for the “Tickler” or feedback coil across the “regenerative feedback” control pot. The waveband switch also adds parallel capacitor on LW.

Front panel Tuning scale

Herge-pale

Print at a suitable size for your front panel. Of course many of these stations don’t exist any more. Athone on LW is actually Summerhill, Near Trim, Co. Meath, Ireland. Home on LW is R4.

herge-radio-1

 Russian Rod Pentode, Uncategorized  Comments Off on herge-radio-1
Apr 042018
 

 We’ll call this 1 valve Regenerative Radio “The Hergé” in honour of his research and attention to detail. (fun stories too)

Hergé wrote that strip (in French) for the Belgian newspaper in 1934 or 1935 just after the Japanese invaded China and blew up the Manchurian Railway.
Tintin is picking up Japanese transmissions to/from spies in China in Morse.
Note DF loop aerial.

The Japanese lodged a protest with the Belgian Embassy after it was published!

It was later coloured and published in English as “The Blue Lotus”. You can buy the full story in most bookshops and online.

The Hergé will be a one valve regenerative Radio running off batteries (3x PP3 = 22.5 / 27V, 6x PP3 = 45V/54V or 8 x PP3 = 60V/72V ). Optionally a second 1j18b can be added as an audio amplifier, especially valuable if you want to use 27V. You can even use 2 x PP3 (16V to 18V) if you add and amplifier. The valves (or Tubes) used are Russian Sub-Miniature Rod Pentodes made entirely for Military use.

Also you can add a 3 x 1j18b Headphone amplifier for ordinary 32 Ohm “player” ‘phones (18V to 45V, 3 x AA cell LT)  or an amplifier with 2 x 1j18b and 1j29b for a loudspeaker (45V to 90V).

You can wire it for LW, MW or SW, or fit a switch for two bands or more.

Unusually much of the wiring will use plastic screw terminal blocks.

Testing the design concept

Valve on IC breadboard!

Basic Radio Concept

The actual  radio “front” is regenerative Tuned Radio Frequency (TRF), The regenerative feedback (using coil labelled Yellow & Blue) cancels out losses in the tuning circuit thus making the tuning sharper and signal stronger. Too much feedback and the circuit is a small MW transmitter! 

Basic concept schematic

Early version of radio. Current version is a little different.

Basic concept. It’s using a valve made in 1980s that was designed in mid 1950s.

Specification

Approximately 170KHz to 270KHz on LW and 550KHz to 1200MHz on MW.

4 x AA Alkaline nominal 6V LT @ 21.5mA  (about 120 hours),

4 x PP3 Alkaline nominal 36V HT @ 700uA  (about 250 hours)

4 x 1j18b valves. (Cost under 3 Euro total excluding postage)

No external aerial or earth required.

Warning!

Note that higher voltages are dangerous, especially above 50V. There is also risk of fire and burns or even explosions if NiMH are used to make higher voltage packs.

Comparison

The latter half 1950s Battery portable radio sets used a loop aerial in the lid. They used 125mA LT 1.5V and about 6.5mA HT from 90V pack. Line up filament Heptode frequency changer / oscillator / mixer. From 1954.”>filament Heptode frequency changer / oscillator / mixer. From 1954.”>DK96, filament direct oxide cathode. Replaced earlier 1T4 / DF91″>filament direct oxide cathode. Replaced earlier 1T4 / DF91″>DF96, DAF96 and DL96. Usually LW & MW.  The earlier 1950s and late 1940s miniature valve sets used filament direct oxide cathode. Equivalent with RCA 1T4. Replaced by 25mA DF96 “>filament direct oxide cathode. Equivalent with RCA 1T4. Replaced by 25mA DF96 “>DF91 which is twice the filament current. They had more variation of valves and design and up to 250mA LT 1.5V current.

The “Hergé” uses 24mA from 4 x AA cells (6V) and about 1mA from  4 x PP3 (36V)

Experimenting with 1j18b

 Experiments, Russian Rod Pentode, Uncategorized  Comments Off on Experimenting with 1j18b
Apr 292014
 

Experimenting with Russian Rod Pentodes

Here is Russian 1j18b (aka 1zh18b, 1sh18b really 1Ж18Б ) on IC breadboard. The 1j24b and 1j29b are actually better purchases.

Testing 5.4MHz Hartley Oscillator at 16V and 25V.

Dscf2010

1j18b with 1.2V NiMH for filament and  +15V to +32V test bench PSU

This valve concept  was invented in 1950s but many models only entered production in early 1960s and used up to 1980s in MIG fighters and portable Military radio. Superior frequency response to many Germanium transistors (120MHz vs 3MHz), more stable, high impedance lack of Silicon Transistor production is many the reason for long term use. No recorded Domestic/Consumer application.

Heater filament power is from 12mW to 50mW depending on model compared with 2000mW for typical US/European domestic valves (tubes). Recommended HT typically 45V (max 60V) to 150V for 4W “transmitter” versions. But operation at 16V upwards is definitely feasible. Apart from the 4W models, the valves are so low power that in some application circuit the power consumption is similar to transistors and the valves can be mounted direct on PCB or stripboard (veroboard). The 1j37 is unusual as although it has single anode it has dual control grids at the same place. Read the Radio Museum article to see how this is possible. Regular valves with a single anode and cathode can’t be made like that. It is like a dual gate depletion mode cascode MOSFET. (A pentode with suitable voltages on the 3 grids behaves like cascode circuit. I think the 1j37b is a pentode with a 2nd identical control grid, not a hexode)

Original circuit from German Website (scroll down)

hartley_orig_dl1adr

For operation at 16V to 32V move R1 grid bias from ground (f-) to +1.2V (f+), makes grid closer to 0V of cathode.

Do not exceed filament)”>filament)”>1.2V filament. These are not 1.5V filaments. For NiMH battery which is a bit more voltage than a NiCd, a 10 Ohm series resistor gave about 1.17 to 1.2V on filament.

See Radio Museum Article

Dscf2009

5.4MHz, 3V RMS on 25V HT (about 1V RMS on 16V HT)

Grounding the Anode and using G2 as anode with 42V HT operation as a Colpits oscillator up to 100MHz is possible. So using it as a triode is possible,