Mazda V888 - UK Vintage Radio Repair and Restoration Discussion Forum

G6Tanuki · 2nd Oct 2014, 8:47 pm

In a cache of valves I've been sorting there's a rather odd beastie.

The Mazda V888 - which I can only conclude was a sort-of 6AM6/EF91-equivalent.

I'm thinking that the paper label makes my example maybe an early-adoption version? Alas I don't have any way to measure its characteristics to see how well it complies with the generic 6AM6/8D3/Z77/EF91

G8HQP Dave · 3rd Oct 2014, 11:54 am

5.7V heater??

G6Tanuki · 3rd Oct 2014, 12:17 pm

That confused me too..!

It was in a box of valves I got from a car-boot sale. Whether the paper label is something that was put there at the factory or was attached by a previous owner I don't know. The paper does appear to be a rather poor-quality and coarse variety so could possibly be something from immediately after WWII ?

Alan Stepney · 3rd Oct 2014, 1:59 pm

http://www.r-type.org/articles/art-148.htm

says it is an EF91, but with no further data.

G8HQP Dave · 3rd Oct 2014, 2:22 pm

My guess is a development version of the EF91(etc.), with a label saying which particular test conditions this sample was used for? If they were testing new cathode coatings a cool heater test might make sense.

AC/HL · 3rd Oct 2014, 3:44 pm

It appears to have been calibrated for a particular application, one of a batch.
That heater voltage would give a known level of emission, which would perhaps remain more consistent with ageing?

boxdoctor · 6th Oct 2014, 11:26 am

Could it have been a special adaptation of the 6AM6 for use in a remote pre-amp, where the heater voltage would be reduced owing to the resistance of the length of the cable?
Marconi/Osram made an R.F. pentode with a 5.7 volt heater, Type KTW73/M. I had one of those many years ago. I've never seen the type number V888 though. Maybe a pre-production sample.

2nd Oct 2014, 8:47 pm	#1
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,010	Mazda V888 In a cache of valves I've been sorting there's a rather odd beastie. The Mazda V888 - which I can only conclude was a sort-of 6AM6/EF91-equivalent. I'm thinking that the paper label makes my example maybe an early-adoption version? Alas I don't have any way to measure its characteristics to see how well it complies with the generic 6AM6/8D3/Z77/EF91 Attached Thumbnails

3rd Oct 2014, 11:54 am	#2
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Mazda V888 5.7V heater??

3rd Oct 2014, 12:17 pm	#3
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,010	Re: Mazda V888 That confused me too..! It was in a box of valves I got from a car-boot sale. Whether the paper label is something that was put there at the factory or was attached by a previous owner I don't know. The paper does appear to be a rather poor-quality and coarse variety so could possibly be something from immediately after WWII ?

3rd Oct 2014, 1:59 pm	#4
Alan Stepney Rest in Peace Join Date: Feb 2008 Location: Dorset, UK. Posts: 947	Re: Mazda V888 http://www.r-type.org/articles/art-148.htm says it is an EF91, but with no further data.

3rd Oct 2014, 2:22 pm	#5
G8HQP Dave Rest in Peace Join Date: Sep 2008 Location: Solihull, West Midlands, UK. Posts: 4,872	Re: Mazda V888 My guess is a development version of the EF91(etc.), with a label saying which particular test conditions this sample was used for? If they were testing new cathode coatings a cool heater test might make sense.

3rd Oct 2014, 3:44 pm	#6
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,643	Re: Mazda V888 It appears to have been calibrated for a particular application, one of a batch. That heater voltage would give a known level of emission, which would perhaps remain more consistent with ageing?

6th Oct 2014, 11:26 am	#7
boxdoctor Rest in Peace Join Date: Sep 2010 Location: Ripley, Derbyshire, UK. Posts: 785	Re: Mazda V888 Could it have been a special adaptation of the 6AM6 for use in a remote pre-amp, where the heater voltage would be reduced owing to the resistance of the length of the cable? Marconi/Osram made an R.F. pentode with a 5.7 volt heater, Type KTW73/M. I had one of those many years ago. I've never seen the type number V888 though. Maybe a pre-production sample.