• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Tube amps with tv tubes

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The Frame deflection tube associated with the CRT yoke in the late 50,s-60,s was the well known PCL85 I lost count of the number I changed due to that fault .


It was superseded by the "improved " PCL805 , it wasn't till later that I found that the design couldn't cope with dual 405/625 switching in UK TV,s in other words the tube was "under-designed " .


I still have several in my junk box.


As this fault seems to be also present in the USA according to Wg_Ski.
The tube was basically an ECL type series with a heater of 18volts for UK series heater TV,s .
After a multitude of complaints the PCL805 was brought out it wasn't a great deal better , this tube was HOT !!! in a TV circuit even cooked associated resistors -typical blackened PCB .
It was made worse by the dual standard ( switchable ) UK TV of 405/625 lines versions ( I owned several ) .


If you look at what it was asked to do in a TV circuit especially switch on from cold you will understand the load it carried.
 
For European viewers US terminology Magnoval is known here as=B9D conforming to the Pro-Electron nomenclature ( Standard,s Body ) I can see the point of Kodabmx,s complaint I was not alone in complaining about the engineering imbalance of a very large tube having small steel pins with the only reinforcement being the glass base ,it got worse with the even heaver later versions used in color TV,s .

Always thought that magnoval was the official socket name, as it is printed on all xL5xx datasheets I have seen.
It's true that the EL/PL509/519 is a bit tall and heavy to be mounted by the socket alone. The Philips and Sylvania datasheets state that 'additional supporting of the tube at the top is required.'
That's something to address with the PL509 amp that I'm planning.
Perhaps combining shielding the topcap connection and supporting the top of the tubes.
 
I personally don't know any tech guy into tubes in the UK using the name "Magnoval " but I realise the US has different designations for tube (valve ) bases .
The standard in the UK was used by Mullard /Mazda etc even the UK Wireless World equivalent books which are available on a very good US website for downloading.
If WW/EW used those designations you can bet all UK engineers used them too including government departments as the AVO VCM was used by them( and me ) and the base designations conformed to UK spec.


The last issue of the PL range had a very large valve/tube ,its size made the small pins look unstable --and were .


I once got a shock from the top cap while repairing a CRT television it was worse than a direct mains shock- it was near 800 volts at a high current luckily it wasn't across my heart just my arm which took a week for the throbbing to stop and was stiff for a while after.
 
My experience has been just the opposite. The big hot octal tubes develop loose bakelite bases when the glue to glass interface fails. So many old octal tubes with adhesive tape wrapped around the base to glass joint. That's why they came up with the octal button bases later, which are more like Compactron bases.

If you have cracked a Compactron, Novar or Magnoval base tube, then you have a bad socket. Lots of old TV sets had cheesy sockets with tin plated socket pins that soldered themselves to the tube pins in the heat. A quality socket doesn't have such problems.

For audio purposes, the lower gm "audio" tubes generally do have a straightforward linearity advantage (if you are not using the extra gm for N Fdbk that is). However, with N Fdbk, even just local N Fdbk, the balance can tip the other way.

This is especially apparent with the latest design developments using TV "Sweep" tubes. Crazy drive has given us constant gm (versus plate current) beam pentodes without even using N Fdbk (feedforward actually).

Then the "new" series Schade local N Fdbk (UnSET, CED) can produce Triodes from "Sweeps" that rival, if not exceed, the best DHT triodes. (no plate curve rollover from mis-match between grid1 and plate or grid2 characteristics, greatly reduced distortion.)

Finally, Crazy Fdbk, combined with the "new" series Schade scheme (UnSET, CED) has now given us "Triodes" with constant gm and straight line plate curves. A Load Invariant constant gm lack of distortion. This is the proverbial "wire with gain". This has long been the mythical Holy Grail of tube design (or any amplifying device). Like Alchemists turning Lead into Gold. It's for real now. These are exciting times for those in the know. I would even say an historic moment.

One can exceed the quality of the best DHT tubes now without having to use extreme HV B+ or high primary Z OTs. One can make a cheap 211 or 212 Amp equivalent for a few hundred $. Without hazardous HV or compromised OT frequency response, and with low output Z. Maybe no flashy big transmitter tube look or heater illumination, but it's now a practical DIY project for everyone. Where is Heathkit when we need them?

a) Crazy drive
b) "new" series Schade (UnSET, CED)
c) Crazy Fdbk with the "new" series Schade drive

d) some $1 TV tubes don't even need any circuit tricks.

just for comparison:

e) 26LX6 native beam pentode mode
f) 26LX6 Crazy drive mode

g) 211 DHT triode

Unfortunately, many of the once low cost TV Sweeps are approaching about 1/2 the price of "audio" tubes now. With demand will come new production eventually, hopefully, like the cap-less PL509.
 

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The capless EL509 was produced by Svetlana under the moniker EL509II but is now out of production as Svetlana has ceased their production of glass tubes. J/J still produces another one called EL509S.
Unfortunately they both are Octal tubes and share the EL34 pinout with the plate pin 3 next to the heater pin 2.
Best regards!
 
The UK produced a EL506 Pentode in the 60,s suitable for audio using the UK standard --B9D base ,this valve/tube was much better designed with the anode/plate on pin 9 with pin 8 as a N/C .
As a matter of fact Mazda /Brimar UK valve/tube factories both produced it and Thorn/EMI a British company produced an audio amplifier circuit for it .


brimar_thorn_va_12_el506_pp_ed_2.png




By the way early design UK/USA valves /tubes of the 20,s/30,s ended up with old school insulating tape round the bases as the methods used to hold them steady were very low grade , so much so if they were moved a few times the internal wiring snapped off near the glass tube section .


I was able to cut the Bakelite out , file down the glass and resolder some of the very old exotic (expensive ) radio types .
 
If you like EL506 ($ 600 Ebay), take a look at the 10JA5 Vertical Sweep ($3 Vacuumtubes.net)

Other than 1/3 the screen V, nearly the same tube.

7868 and 7591 are similar too. (and same screen V)

The Russian 6P41S works very well, if the G2 voltage is limited to half the anode.
The connection of the base (both tubes are MAGNOVAL) EL506 and 6P41S is the same!
 
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6FM7 dissimilar triode

Hi

The 6fm7 is the compactron sister of 6em7.

The 6EM7 is getting costly in last few years hence the recommendation to look at 6FM7.

This is a vertical deflection amplifier and driver in a single bottle.

This is a very good sounding tube SE or PP, anode or cathode parafeed configuration - highly recommended.

BR

Glass painter
 
TOO LATE!!! :eek:

$130 for 5 of them (6FM7) at 15% discount on Ebay!

The original 6EM7 look to be cheaper.

Glad I bought a box of them back when they were $1 each (6FM7, 6GF7).

I knew it was going to be that bangybang tubes scammer. He sells everything at inflated prices and people fall for it. His listings even show up in places like walmart! Someone has to be laundering money 2 Vintage General Electric 6AL5/6663 Double Diode Detector Tube Valve - BangyBan | eBay
 
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