PL-519 Tube - Tell me more please...

[GlidingDutchman]

Hi all, I have been away from this place for a very long time... good to be back.

I have a few questions on the (in)famous PL-519 tube/valve.

Am I correct when I say it is more like a "beam tetrode"? (KT type tubes in structure...?)

What is the closest common replacement for it?

In UL mode how many watts can teoretically be pulled from a pair of PL-519s?

Best recommended driver stage tubes? "5751 JAN"?

The reasons for these questions... ? I have received a scrappy amp from a friend thats in need of a rebuild. It uses two pairs of PL-519 tubes. The one set has burnt (one tube actually melted!!)

Cheers
GD

[ilimzn]

Originally posted by GlidingDutchman
Am I correct when I say it is more like a "beam tetrode"? (KT type tubes in structure...?)

It IS a beam tetrode, says so right in the datasheet
It is the largest european horizontal sweep tube, which means it was originally intended to operate as a switch of sorts, so not for linear operation.

What is the closest common replacement for it?

It is rather unique. it has no direct replacements although a PL509 or 6P45S may be used instead. There are some US sweep tubes (which are becoming increasingly rare and expensive) that are similar.

In UL mode how many watts can teoretically be pulled from a pair of PL-519s?

Being a sweep tube, it has a very high steepness and low maximum Vg2 rating which makes it unsuitable for UL operation, or, more precisely, inefficient. It IS capable of working quite well with cathode feedback, which unless Vg2 is bootstrapped, includes UL operation as well. In class (A)B pentode mode it should be capable of well in excess of 100W, more with screen drive. With straight UL the low screen voltage automatically means low anode voltage and limits output to perhaps 30-40W. It is possible to somewhat stretch the G2 rating if operated in triode mode but not advisable. These tubes can easily go into runaway, especially if fixed bias is used. But, with sane limits, About 12W SE (Maybe 15 if pushed real hard) and 30W PP in triode is possible. Keep in mind that parameter variatins between tubes are quite large, 30% is typical. I managed to get one decent pair out of 20 tubes...

Best recommended driver stage tubes? "5751 JAN"?

Something capable of swinging some 150Vpp or so... input capacitance is quite high in triode mode but mu is low (about 3). A lot less drive is needed in pentode, and even in screen drive you may get away with less, but you do need quite a lot of current.

The reasons for these questions... ? I have received a scrappy amp from a friend thats in need of a rebuild. It uses two pairs of PL-519 tubes. The one set has burnt (one tube actually melted!!)

Yes, when these tubes run away, they are perfectly capable of melting the envelope. The russian 6P45S has a much more sturdy envelope but also a different construction and slightly lower dissipation (at least on paper). The glass is so much thicker the whole tube weighs nearly double compared to a EL/PL509/519.

[GlidingDutchman]

ili,

Thank you for the reply!

Urgh... looks like I am not going to get far with this amp...

I wonder if I can use the OTPs with different tubes. EL84's perhaps?

Here is pics of the amps internals:

[Wavebourn]

What voltages are available: anode, screen, bias? Can you measure them?

[GlidingDutchman]

Originally posted by Wavebourn
What voltages are available: anode, screen, bias? Can you measure them?

Mmm... I could not measure it because the amp had a few shorted wires (the manufacturer decided NOT to use tube sockets for the PL-519s and thus there were a few tags touching after I removed the faulty tubes). I didnt want to risk losing any tranfos so I snipped off the power cord to keep all safe.

Neg bias I estimate to be -100vdc
Anode around 200vdc (PSU caps are rated 250v, 2200uF Matsushita devices).
Could double up to 400vdc (two independant HT widings on transfo)... I hope!
Screen I dont know.

Driver stage I guess to be 250vdc or 300vdc regulated.

I am busy noting the schematic and will post it in due time. Hope I got everything right on paper...

KT88 tubes look like they can be used with these OPTs. Or 4 EL34 in PP mode.

GD

[ilimzn]

Depends on what mode of operation was chosen for the tubes. These types generally work at low voltages (hence 200V supply) but high currents, which means Raa on the trafos will be quite low. In triode mode Ra of the tubes is about 275ohms so the trafos will be low ratio, it is questionable if you will be able to use them with other tubes.

[Wavebourn]

I would consider to use 6V6 with some MOSFETs in Darlington configuration, they would fit nice.

Edit: is it possible to order some custom aluminium alloy parts in Midrand?

[GlidingDutchman]

Originally posted by Wavebourn
I would consider to use 6V6 with some MOSFETs in Darlington configuration, they would fit nice.

Edit: is it possible to order some custom aluminium alloy parts in Midrand?

MOSfet...? Now that sounds interesting... What about a pure MOSfet output stage using the OPTs? Ultra neo-classic...! He-he!

There is a place here in Pretoria that does CNC machining - they are equipped with a 5-axis CNC machine, laser cutters, CNC lathes etc. They do work for the SA military.

[Wavebourn]

Originally posted by GlidingDutchman


MOSfet...? Now that sounds interesting... What about a pure MOSfet output stage using the OPTs? Ultra neo-classic...! He-he!

There is a place here in Pretoria that does CNC machining - they are equipped with a 5-axis CNC machine, laser cutters, CNC lathes etc. They do work for the SA military.

I'm afraid it would cost lot of Rands to order heatsinks for your amp there...

You can use pure MOSFETs, but they have high non-linear input capacitances, also because of high transconductances Miller capacitances would be too high. Darlingtons made of pentodes+MOSFETs are easy to drive and sound nice.

[Allen Wright]

You ask, how many watts can be pulled in UL?

The answer is NONE, as the tube has a very low screen voltage rating (275) and hence can't be used in UL unless you have avery complex OPT with a speparate screen winding.

How power can you pull from this tube in some other configuraion?

Tim de Paravacini gets 200 watts from two pairs in a quasi MacIntosh topology

Melos got an unbelievable 400 watts from two pairs in screen drive format!

I measted this on a pair we had here, a real 400 watts!

It's a great tube and can sound good, but the low screem volts make it award to use in most circuits, and they are VERY hard to buy these days in any sort of quantity, all having gone into Ham transmitters.

Regards, Allen (Vacuum State)