Replacing a UL84 valve. with a PL84

[clockman]

Hi for my Easter project i have been reading a early thread on the failure rate of the UL84 valve so have used a new PL84 and a small 15 volt heater transformer from my spare parts box. As there is a lot of spare room on this chassis for a TX. Set now working fine and no other parts needed.

[Sideband]

So what value resistor have you fitted in place of the UL84 heater?

[clockman]

Hi i used Paul Stenning`s exelent Exel spread sheet that i have on my computer it was a dropper value 1.170 K ohms 12 watts i also used the TX to power the 2 dial lamps .TAB

[clockman]

My reason was a used UL84 cost £16 on ebay a new PL84 cost £6 on the same site if i had needed one ?

[Chris55000]

Hi!

Whilst the EL84 and UL84 were directly equivalent, for some strange reason Mullard stated the PL84 was primarily intended as a field TB output valve, the PL82 was the recommended audio type!

However the data in the Philips sheet does state that the PL84 can be used for either purpose, but not in the British Mullard book!

Chris Williams

[JonSnell]

I still regularly service a couple of Dansette record players and they have their original UL84s.
Dating back from 1957.

[Robert Gribnau]

Originally Posted by Chris55000

Whilst the EL84 and UL84 were directly equivalent, for some strange reason Mullard stated the PL84 was primarily intended as a field TB output valve, the PL82 was the recommended audio type!

The UL84 is not directly equivalent to the EL84.

Strangly enough the EL86, PL84 and UL84 are (except for heater requirements) equivalent to eachother. The EL84 does not have an equivalent in de P or U range of valves.

[snowman_al]

Originally Posted by clockman

Hi i used Paul Stenning`s exelent Exel spread sheet that i have on my computer it was a dropper value 1.170 K ohms 12 watts i also used the TX to power the 2 dial lamps .TAB

Am I missing something here? I cannot 'see' your calculator. But,
The U series valves have a current of 0.1A, so a 45volts drop at 0.1A needs 450Ω. 470Ω 6 or 7 watts is close enough.
1.17K drops you 117 volts...

[Station X]

Originally Posted by snowman_al

Am I missing something here? I cannot 'see' your calculator. But,
The U series valves have a current of 0.1A, so a 45volts drop at 0.1A needs 450Ω. 470Ω 6 or 7 watts is close enough.
1.17K drops you 117 volts...

See here:-

https://www.vintage-radio.com/repair...per-calcs.html

[snowman_al]

Thanks Graham,
So using the 'Single Resistor' calculator (ohms law), assuming only the UL84 is changing you need to drop 45 volts. So Vh over Ih = Rd. 45v over 0.1A = 450Ω
Similarly Vh x Ih = Pd 45 x 0.1 = 4.5 Watts.

As I mention, just for the single change of the UL84. If other changes were needed the calculations will be different, but that is not obvious from the description, hence my question.

Alan

[ms660]

Don't worry Al, you're posts tell me you're still in the land of the sane.

Lawrence.