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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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2nd Apr 2021, 9:43 pm | #1 |
Pentode
Join Date: Jul 2020
Location: Borehamwood, Hertfordshire, UK.
Posts: 216
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Replacing a UL84 valve. with a PL84
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.
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2nd Apr 2021, 10:41 pm | #2 |
Dekatron
Join Date: Oct 2003
Location: Croydon, Surrey, UK.
Posts: 7,580
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Re: Replacing a UL84 valve. with a PL84
So what value resistor have you fitted in place of the UL84 heater?
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3rd Apr 2021, 2:11 pm | #3 |
Pentode
Join Date: Jul 2020
Location: Borehamwood, Hertfordshire, UK.
Posts: 216
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Re: Replacing a UL84 valve. with a PL84.
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
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3rd Apr 2021, 2:15 pm | #4 |
Pentode
Join Date: Jul 2020
Location: Borehamwood, Hertfordshire, UK.
Posts: 216
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Re: Replacing a UL84 valve. with a PL84
My reason was a used UL84 cost £16 on ebay a new PL84 cost £6 on the same site if i had needed one ?
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4th Apr 2021, 11:57 am | #5 |
Nonode
Join Date: Aug 2007
Location: Walsall Wood, Aldridge, Walsall, UK.
Posts: 2,874
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Re: Replacing a UL84 valve. with a PL84.
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
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4th Apr 2021, 12:27 pm | #6 |
Hexode
Join Date: Oct 2019
Location: Weymouth, Dorset, UK.
Posts: 477
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Re: Replacing a UL84 valve. with a PL84
I still regularly service a couple of Dansette record players and they have their original UL84s.
Dating back from 1957. |
4th Apr 2021, 12:35 pm | #7 | |
Heptode
Join Date: May 2017
Location: Konongo, Ghana
Posts: 516
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Re: Replacing a UL84 valve. with a PL84.
Quote:
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.
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4th Apr 2021, 1:38 pm | #8 | |
Octode
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 1,092
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Re: Replacing a UL84 valve. with a PL84.
Quote:
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...
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4th Apr 2021, 2:21 pm | #9 | |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,289
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Re: Replacing a UL84 valve. with a PL84.
Quote:
https://www.vintage-radio.com/repair...per-calcs.html
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Graham. Forum Moderator Reach for your meter before you reach for your soldering iron. |
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4th Apr 2021, 2:37 pm | #10 |
Octode
Join Date: Dec 2018
Location: Llandeilo, West Wales, UK.
Posts: 1,092
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Re: Replacing a UL84 valve. with a PL84
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
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4th Apr 2021, 2:43 pm | #11 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Replacing a UL84 valve. with a PL84
Don't worry Al, you're posts tell me you're still in the land of the sane.
Lawrence. |