Will the real 6V4 please step forward - UK Vintage Radio Repair and Restoration Discussion Forum

retailer · 11th Sep 2018, 6:50 am

Going through and sorting a box of used valves I picked up what looked like an EZ81/6CA4, turning it over I saw it labeled 6V4 the European designation being EZ80, having just fished out a 6V4 a few minutes earlier I placed them together - clearly only one of them is a EZ80/6V4, I strongly suspect the larger one is an EZ81 it is not only taller, and has larger anodes but looks identical to the other EZ81's I have, was it labeled incorrectly ? it may have been but probably not, production costs of each must have been very similar so it was more likely that re-labeling was a cheaper option than stopping a production line and resetting it for what was essentially the same valve with higher specs.

It was very dirty with that greasy type of dirt that seems to be attracted to valves, strangely I managed to clean it with water and paper towel enough the get a photo with wiping off any of the label, I have other valves (and I'm sure others do as well) where the labels seem to magically disappear right before your very eyes, the very act of just removing them from the box is enough to almost wipe the complete label off.

joebog1 · 11th Sep 2018, 10:22 am

6CA4 in aussie speak is the superior valve. NEC made the best of them in my experience.
6V4 is a "radio" valve for moderate currents.
6CA4 is an "amplifier" valve for larger currents.
BOTH are small rectifiers. Akai Tape recorders ( valve types, or at least hybrid types) used 6CA4's in abundance.
BOTH run bl**dy hot if run at maximum ratings, but the 6CA4 didnt fail.

< ex service manager Akai )

Joe

G8HQP Dave · 11th Sep 2018, 9:20 pm

Rectifiers from different factories may have different anode shape/size yet still have the same rating. EZ80 and EZ81 have different heater current too, so they are not necessarily directly swappable.

retailer · 12th Sep 2018, 6:53 am

Quite possibly my 6CA4 in 6V4 clothing was mistakenly labeled as a 6V4, I do believe though it is a 6CA4, I tried both valves in a HV power supply that I have and was able to separate the filament leads enough to get a clamp meter around one of them, even though the smallest range is 6 amps ac I was able to see that the larger valve drew almost twice the heater current of the smaller valve, this ties in with the info in my valve data manual - 1amp against 600mA. In a real life situation the extra 400mA of heater current would probably not unduly stress the transformer unless it was already a marginal design and right on the limit of it's ratings.

turretslug · 12th Sep 2018, 9:51 am

That bigger "6V4" is striking in that it looks to be similar in construction to "Rimlock" (B8a) valves, i.e. a separate hard glass base secured to the bulb with lower-melting-point frit- perhaps the glass equivalent of soldering, as opposed to the welding of the later miniatures! From what I've seen of EZ81s, they have a more complex anodes finning array, resulting in a six-sided "snowflake" arrangement viewed from above, as compared to the EZ80's cruciform arrangement. Perhaps this is an early/developmental 6V4/EZ80 with a more consumptive heater?

Anecdotally, I've noticed that it's not unusual to find the EZ81 fitted in things where an EZ80 is specified and adequate- perhaps they were plentiful or easily procured? I find it difficult to believe that they would have been cheaper. The EZ81's ratings are such that it was intruding on GZ34 territory- perhaps Mullard over-produced expecting that this miniature valve with its 6.3W consumption heater would be more successful at displacing the IO 9.5W type than was actually the case, with equipment manufacturers preferring to trust the longevity of the bigger envelope valve with its "traditional" separately fed 5V heater?

G8HQP Dave · 12th Sep 2018, 2:41 pm

I seem to recall seeing an RFT EZ80 which looked internally more like an EZ81. Maybe just conservative engineering? Or is it that some Eastern bloc valves were more like substitutes for Western types rather than exact equivalents?

G6Tanuki · 15th Sep 2018, 3:00 pm

I can readily imagine that at some time in the production lifespan of things like the EZ80/81 it would have become more-economical to combine the production-lines and produce only the higher-performing valve for use in all applications rather than having two lines running. The 'fixed costs' [glassblowing, electrode-assembly, pumping] would have been the same for both valves, after all.

Better to have one production-line running at full capacity than two lines running at half-capacity.

11th Sep 2018, 6:50 am	#1
retailer Heptode Join Date: May 2005 Location: Adelaide, South Australia Posts: 541	Will the real 6V4 please step forward Going through and sorting a box of used valves I picked up what looked like an EZ81/6CA4, turning it over I saw it labeled 6V4 the European designation being EZ80, having just fished out a 6V4 a few minutes earlier I placed them together - clearly only one of them is a EZ80/6V4, I strongly suspect the larger one is an EZ81 it is not only taller, and has larger anodes but looks identical to the other EZ81's I have, was it labeled incorrectly ? it may have been but probably not, production costs of each must have been very similar so it was more likely that re-labeling was a cheaper option than stopping a production line and resetting it for what was essentially the same valve with higher specs. It was very dirty with that greasy type of dirt that seems to be attracted to valves, strangely I managed to clean it with water and paper towel enough the get a photo with wiping off any of the label, I have other valves (and I'm sure others do as well) where the labels seem to magically disappear right before your very eyes, the very act of just removing them from the box is enough to almost wipe the complete label off.

11th Sep 2018, 10:22 am	#2
joebog1 Banned Join Date: Jun 2015 Location: Mareeba, North Queensland, Australia Posts: 2,704	Re: Will the real 6V4 please step forward 6CA4 in aussie speak is the superior valve. NEC made the best of them in my experience. 6V4 is a "radio" valve for moderate currents. 6CA4 is an "amplifier" valve for larger currents. BOTH are small rectifiers. Akai Tape recorders ( valve types, or at least hybrid types) used 6CA4's in abundance. BOTH run bl**dy hot if run at maximum ratings, but the 6CA4 didnt fail. < ex service manager Akai ) Joe

11th Sep 2018, 9:20 pm	#3
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Will the real 6V4 please step forward Rectifiers from different factories may have different anode shape/size yet still have the same rating. EZ80 and EZ81 have different heater current too, so they are not necessarily directly swappable.

12th Sep 2018, 6:53 am	#4
retailer Heptode Join Date: May 2005 Location: Adelaide, South Australia Posts: 541	Re: Will the real 6V4 please step forward Quite possibly my 6CA4 in 6V4 clothing was mistakenly labeled as a 6V4, I do believe though it is a 6CA4, I tried both valves in a HV power supply that I have and was able to separate the filament leads enough to get a clamp meter around one of them, even though the smallest range is 6 amps ac I was able to see that the larger valve drew almost twice the heater current of the smaller valve, this ties in with the info in my valve data manual - 1amp against 600mA. In a real life situation the extra 400mA of heater current would probably not unduly stress the transformer unless it was already a marginal design and right on the limit of it's ratings. Attached Thumbnails

12th Sep 2018, 9:51 am	#5
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,393	Re: Will the real 6V4 please step forward That bigger "6V4" is striking in that it looks to be similar in construction to "Rimlock" (B8a) valves, i.e. a separate hard glass base secured to the bulb with lower-melting-point frit- perhaps the glass equivalent of soldering, as opposed to the welding of the later miniatures! From what I've seen of EZ81s, they have a more complex anodes finning array, resulting in a six-sided "snowflake" arrangement viewed from above, as compared to the EZ80's cruciform arrangement. Perhaps this is an early/developmental 6V4/EZ80 with a more consumptive heater? Anecdotally, I've noticed that it's not unusual to find the EZ81 fitted in things where an EZ80 is specified and adequate- perhaps they were plentiful or easily procured? I find it difficult to believe that they would have been cheaper. The EZ81's ratings are such that it was intruding on GZ34 territory- perhaps Mullard over-produced expecting that this miniature valve with its 6.3W consumption heater would be more successful at displacing the IO 9.5W type than was actually the case, with equipment manufacturers preferring to trust the longevity of the bigger envelope valve with its "traditional" separately fed 5V heater?

12th Sep 2018, 2:41 pm	#6
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Will the real 6V4 please step forward I seem to recall seeing an RFT EZ80 which looked internally more like an EZ81. Maybe just conservative engineering? Or is it that some Eastern bloc valves were more like substitutes for Western types rather than exact equivalents?

15th Sep 2018, 3:00 pm	#7
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 13,995	Re: Will the real 6V4 please step forward I can readily imagine that at some time in the production lifespan of things like the EZ80/81 it would have become more-economical to combine the production-lines and produce only the higher-performing valve for use in all applications rather than having two lines running. The 'fixed costs' [glassblowing, electrode-assembly, pumping] would have been the same for both valves, after all. Better to have one production-line running at full capacity than two lines running at half-capacity.