Series heaters.

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al newall
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#1 Series heaters.

Post by al newall »

Two valves with the heaters wired in series. In this case ECF80s just for testing.
V1 measures 6.5v
V2 measures 6.39v
Only the heaters are connected at this time.

Is this acceptable and why the discrepancy between the two?
Will these figures change when the valves are fully connected in circuit?
These tubes will be substituted for 6n6p which draw roughly twice the current i think.
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#2

Post by Andrew »

Hi Al,

One valve must have a slightly higher resistance heater than the other, that's all, I wouldn't worry about it. The two valves are simply forming a potential divider, take them out and measure the R of each heater. I would expect them to be off by roughly the ratio you have seen, (R1 + R2)/R1.

What's the current draw of the test valve? 6N6P draw is quite a bit higher that traditional small signal valves which tend to be 300-350mA. I think 6N6P might draw about 800mA each. Given you're slightly over voltage at the mo' then the extra draw will be probably get you closer to ideal 6.3v perhaps even below, depending how good the regulation is on your filament TX.

cheers,

-- Andrew
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Nick
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#3

Post by Nick »

Is this acceptable and why the discrepancy between the two?
The E valves are designed for a 6.3V heater, they are not intended to be used in series. So using them in series will cause different voltage across them. They are designed for a parallel supply, 6.3v across them all/

If this is important, I don't know.

The P series (for comparison) were designed for series use, 300ma through each valve. Each valve at that current may create an 8v or different voltage drop.
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al newall
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#4

Post by al newall »

Thanks.
Good information chaps.

Proved by substituting the 6n6s, which gave me an overall volt drop from 6.5v to 5.2v and equal voltage on V1 and V2.
Changing from a 8R series resistor to 3.9R gives me 6.36v on both when the tubes are warm.
Doubt if i'll get much closer than that.

Cheers.
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#5

Post by Andrew »

Seems 6N6P are OK heated series or parallel as long as the resistance of the heaters are the same, whic in the E series is obviously not gauranteed.

I mean, I don't see how the valve would know, it just sees 6.3v across its pins.

The problem with series, of course, is like old fashioned Xmas tree lights, one out, all out.

cheers,

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al newall
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#6

Post by al newall »

The problem with series, of course, is like old fashioned Xmas tree lights, one out, all out.
Suppose its a chance you take.
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#7

Post by Nick »

I mean, I don't see how the valve would know, it just sees 6.3v across its pins.
It doesn't, it more to do with how its designed to be used, if you run a parallel heated valve in series, you can not just expect them all to have the correct voltage, in the same way, connecting series valve in parallel is equally unsure.

For example, the PCC88 will draw its 300ma when it has 7.6 volts across it, but the PCF82 will pass 300ma with 9v across it.
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Paul Barker
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#8

Post by Paul Barker »

al newall wrote:
The problem with series, of course, is like old fashioned Xmas tree lights, one out, all out.
Suppose its a chance you take.
Might be an advantage to have them all go down with one.
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#9

Post by Nick »

Might be an advantage to have them all go down with one.
Yep, but then you have to work out which one. (still like the xmas lights).
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#10

Post by Paul Barker »

Yes TV repair man used to have a brief case full of P valves, just kept changing valves 'till he got the right one, job's a goodun.
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#11 Valves in series/parallel

Post by John Caswell »

Hi all ,
There seem to be a some odd ideas here. What Nick says is not strictly correct
There were several ranges of valves available, not all listed here -

6.3V heater types which were usually used in parallel voltage fed systems so current draw would vary by type and they were normally designated 6*** with a few exceptions such as the 12***.

Then there were the "P" range of valves with varied heater voltages but all were 300mA current rated generally for use in television where they were current fed in a series chain via a dropper resistor/transformer and a thermistor/NTC to limit the switch on surge.

The "L" series eg UL41 were primarily radio valves used similarly to the "P" series but with heaters rated at 100mA current.

There were also the battery set valves eg DK91/96, DL 91/92/96 etc all basically designed for 1 .4V parallel heater supplies but in pretty well all cases used in a series heater chain so the lower current valves DK91/DF91/DAF91, had parallel resistors across their heater to compensate for the extra current taken by the output valve (DL**)

Very often valves like the ECC** ranges would used in series chains, where nothing else was suitable/available, as their heaters could be either 6.3V 300mA where both sections were in parallel or 12.6 V 150mA where both were in series and a compensation resistor fitted in parallel across the heater to drop the extra 150mA.
Although, say, a PCC88 is theoretically identical to an ECC88 as far as characteristics are concerned (not heater voltages) I have often found when looking at data that there are subtle differences usually in max anode current/voltage and dissipation limits.

In the instance given, I feel the two ECF80s should be run from 6.3V to allow them to reach correct heater temperature.

As for Paul's "Yes TV repair man used to have a brief case full of P valves, just kept changing valves 'till he got the right one, job's a goodun". As I used to be a "TV Repairman" from 1958-73, and learned a lot of my valve /electronics skills from an Old time TV repair man I take umbrage at that comment.

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#12 Re: Valves in series/parallel

Post by pre65 »

John Caswell wrote:
As for Paul's "Yes TV repair man used to have a brief case full of P valves, just kept changing valves 'till he got the right one, job's a goodun". As I used to be a "TV Repairman" from 1958-73, and learned a lot of my valve /electronics skills from an Old time TV repair man I take umbrage at that comment.

John Caswell
Hi John-in the same vein respectable trades people like Paul, must squirm when "cowboy" builders,plumbers etc etc are exposed on the TV.

Although in your day training was very thorough i'm sure there must have been persons like Paul described so there is no need to take umbridge.

Being old enough to remember valve tellys i have no doubt that to diagnose faults and effect repairs required a great deal of skill,and knowledge which from your reputation have served you (and most of us) well.
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#13

Post by Nick »

What Nick says is not strictly correct
Which bit?
Very often valves like the ECC** ranges would used in series chains, where nothing else was suitable/available, as their heaters could be either 6.3V 300mA where both sections were in parallel or 12.6 V 150mA where both were in series and a compensation resistor fitted in parallel across the heater to drop the extra 150mA.
Whay you mean like a ECC88, ECC40, ECC32 etc. AFAIK E = 6.3v. the 81,82 and 83 and the variants seem to be the exception not the rule in this case.
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#14 Valves in series/parallel

Post by John Caswell »

I did qualify it by adding further ... 6.3V 300mA where both sections were in parallel or 12.6 V 150mA where both were in series and a compensation resistor fitted in parallel across the heater to drop the extra 150mA. Thereby I guess eliminating such valves as mentioned I don't know.

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#15

Post by Nick »

It seems to me John, your real comment was that the E range was 6.3v and 12.6v, AFAIK, thats only true for a small range of valves (3 I think).

A am happy to be wrong about things, thats the way I learn, but I still havent seen which part of my post you found is not "strictly correct", unless you mean the fact that ecc83 can be used with a 12v heater. I think given the small number of valves that fit your description, there is a case of pot and kettle involved there.

Aa far as I know this is the way the philips/mullard type definitions work

http://www.tubecollector.org/documents/numbers-3.htm
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