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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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Old 12th Jul 2012, 9:59 am   #1
Neil Purling
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Default EZ80 Question

Is it practical, i.e. safe to run a EZ80 rectifier from the same LT winding as the rest of the heaters? I don't regard it as being an ideal situation, but I might have to press that ex-Phillips transformer into service. I have no idea which model of Phillips equipment it came from to gauge the LT & HT rating.
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Old 12th Jul 2012, 10:10 am   #2
paulsherwin
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Default Re: EZ80 Question

Yes. Indirectly heated rectifiers like the EZ80 were specifically developed so that they could use the same heater supply as the other valves. Watch the total heater supply loading though.

Using a separate winding does reduce the voltage stress on the rectifier, but it's not essential with these types.
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Old 12th Jul 2012, 2:57 pm   #3
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Default Re: EZ80 Question

Don't know if you already have an EZ80 but the 6X5 (generally in small tubular GT format) has similar general ratings to the EZ80, including good heater-cathode voltage rating, but with an octal base. It's available in reputable brand NOS for a very good price still, although it is on the fringes of the audiophools' radar (pre-amps, etc.)...

Colin.

Update: Suggested max DC output current of 70, rather than 90mA. Sorry.

Last edited by turretslug; 12th Jul 2012 at 3:01 pm. Reason: Doziness!
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Old 12th Jul 2012, 9:28 pm   #4
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Default Re: EZ80 Question

Hi Neil,

A Philips EZ80 is specified to withstand a maximum of 500V between heater and cathode. The heating time required before emission begins is longer than other valves in the set so as to offset the possibility of exceeding the ratings particularly when used at its absolute maximum anode input voltage of 350v rms.

Heater current is 0.6A so not a huge overhead. If you know what valves were used in the original Philips equipment then it will be relatively straightforward to estimate the current rating of the transformer heater winding.

If you are concerned about a heater to cathode short eventually occurring in the EZ80 then it is possible to protect the transformer by wiring a fuse between HT centre tap and chassis/ground 0V, assuming a full wave configuration is used. It will also be a good idea to connect one side of the heater wiring (or the heater centre tap if the transformer has one) to 0V so as to protect the other valves under fault condition.

Cheers

Rich
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Old 12th Jul 2012, 10:52 pm   #5
Leon Crampin
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Default Re: EZ80 Question

I have never, ever seen an EZ80 or 81 fail with a heater cathode short. Millions of sets were produced using this valve with a common heater line.

Leon.
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Old 13th Jul 2012, 10:17 am   #6
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Default Re: EZ80 Question

What the heater-cathode insulation of an EZ80 in an earthed, parallel heater circuit gets subjected to is actually less severe than the heater-cathode insulation of a UY85 in an AC/DC set.

The cathode will be held by the reservoir cap at +200V or so; and the heater (which is usually at the high end of the chain, and assuming a typical line-up of UCH81 UF89 UBC81 UL84 UY85) will go down to -180V or so in the trough of the cycle. So the heater-cathode insulation must withstand the best part of 400V. An FM set with a UABC80 instead of the UBC81 and an additional UCC85 will stress the insulation by an extra 60 volts.

The EZ80 H-K insulation will only ever see about 9V more than the set's HT in the trough of the cycle.
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Old 13th Jul 2012, 10:55 am   #7
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Default Re: EZ80 Question

If using a 6X5 (suggested by turretslug) then put fuses in the anode leads if you value your HT transformer as they are notorious for developing heater/cathode shorts. I have a couple of examples with shorted heater/cathode in my 'dead valve' box.

Adrian.
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Old 13th Jul 2012, 12:13 pm   #8
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Default Re: EZ80 Question

Point taken and thanks, Id come to regard them as a useful little valve for low power gizmos but I always go very conservatively with HT ratings.

Colin.
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Old 13th Jul 2012, 5:51 pm   #9
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Smile Re: EZ80 Question

Hi,
Just as an aside, I have here an old French TV set with a transformer power supply and full wave rectification using two EY82s. I've seen PY82 rectifier valves in British AC/DC tellies (sometimes two in parallel), but never an EY82. Are these a European oddity, or did any British equipment use them?
Cheers, Pete
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Old 14th Jul 2012, 12:40 am   #10
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Default Re: EZ80 Question

Radiomuseum only lists 9 sets using this valve, all TVs, 7 French and 2 Italian.

None of Frank's datasheets is in English except the trilingual Philips one.

Maybe it had other, non domestic applications.....
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Old 15th Jul 2012, 5:24 am   #11
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Default Re: EZ80 Question

Early 1950s Philips literature on its then-new world series TV valves mentions that most P-types had equivalent E-types. Thus perhaps the EY82 was developed simply as a matter of course as the PY82 counterpart, the latter being the standard rectifier valve in the initial TV series, and normally used in pairs. It could be that some manufacturers wanted their AC-only receivers to have as much commonality as possible with their AC-DC models, hence the choice of an EY82 pair, albeit configured full-wave not parallel half-wave.

I don’t think that there were any B9A-based full-wave rectifiers that would have done the job in terms of current capacity, so absent an EY82 pair, moving up to one of the big octal-based rectifiers such as a GZ32 would have been necessary, and with its 5 V heater supply requirement this could well have been seen as an unnecessary complication.

Paucity of the EY82 in UK equipment may reflect the scarcity of AC-only mains isolated TV receivers in the valve era. For regular radio receivers the EZ40, EZ80 and EZ81 were adequate. For more sophisticated radiogram chassis and audio equipment, moving up to a GZ3x seemed to be the norm, as was also the case for the more complex communications receivers.

Just speculation, of course; post facto rationalization of the available scraps of evidence.

Cheers,
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Old 15th Jul 2012, 12:52 pm   #12
Leon Crampin
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Default Re: EZ80 Question

I seem to remember a Philips article somewhere suggesting that a pair of EY82s will out-perform a GZ32 and similar devices in terms of forward voltage drop. Judging by the performance of the PY82, I would suggest they were right. The total heater power at 11.4W for a pair is about the same though.

Philips were always hopelessly valve-oriented, neglecting for instance, the cost of the valve holders and the added assembly time when proposing this two-valve solution. Probably their worst valve-centric error was the fitting of a CRT to the Mullard valve tester when a meter would have done a far better job. They were thoroughly out-smarted by AVO's patents anyway.

Before the final death of the thermionic mains rectifier in TVs caused by the introduction of the silicon diode, Philips must have realised that fitting two devices was a waste of time and money - hence the PY33, which was a lower impedance version of the PY32.

I don't really know why they bothered to make an EY82 - an EZ81 with the anodes connected together will do the same job.

Leon.
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Old 16th Jul 2012, 4:34 am   #13
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Default Re: EZ80 Question

Perhaps an accident of chronology? The PY82 dates from 1951, and very likely EY82 is either a contemporary or a close follower. The EZ81 seems to have appeared around 1956. Possibly amongst other reasons Philips/Mullard wanted to offer a noval-based full-wave rectifier that could power radio/audio equipment with push-pull EL84 outputs. Previously I think that the GZ30 had been suggested for this role.

The EZ80 looks to have been the first Philips/Mullard noval-based full-wave rectifier around 1953, maybe not too much different to the earlier EZ40. The rationale for a rebased version could have been to allow an all-noval line-up for FM-AM receivers (along with the ECC85, ECH81, EF85, EABC80 and EL84), this being the first stage of the Rimlock-to-noval transition for the radio valves.

Cheers,
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Old 16th Jul 2012, 5:01 pm   #14
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Default Re: EZ80 Question

Quote:
If using a 6X5 (suggested by turretslug) then put fuses in the anode leads if you value your HT transformer as they are notorious for developing heater/cathode shorts
Seconded
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