Tesla blue top or red top cross swords ?

[andyrlb]

I have 2 pairs of each of the above that are all nos , which would be considered the better for use in my hybrid preamp?

https://uploads.tapatalk-cdn.com/20200417/31a89939e07a9d1ecbf81baeb70c8546.jpg
https://uploads.tapatalk-cdn.com/20200417/27a4db879424b0dd7266bc85e7cfedd1.jpg
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https://uploads.tapatalk-cdn.com/20200417/91715683d14454e7228c568165935ff5.jpg


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[User211]

Why ask just plug them in and compare?

I'll post some extra info in a bit.

My guess is both pairs will be outstanding just because, well, they are outstanding valves.

I just got these today... Tesla PX25 equivalent.
https://uploads.tapatalk-cdn.com/20200417/d38f28dafc7b057ddbec0236f00fad0d.jpghttps://uploads.tapatalk-cdn.com/20200417/3fe99ee9eef86c09006001bec181e6a7.jpg

[andyrlb]

Why ask just plug them in and compare?

I'll post some extra info in a bit.

My guess is both pairs will be outstanding just because, well, they are outstanding valves.

I just got these today... Tesla PX25 equivalent.
https://uploads.tapatalk-cdn.com/20200417/d38f28dafc7b057ddbec0236f00fad0d.jpghttps://uploads.tapatalk-cdn.com/20200417/3fe99ee9eef86c09006001bec181e6a7.jpg

I ask because it’s to go in a hybrid preamp which means unplugging everything to get to it and then removing 12 screws and the the reverse, so much easier to tap into someone’s knowledge and stick with the one .
[emoji1303]


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[User211]

Something I got from a CZ Tesla vendor. Sorry about formatting:

"yes, people like the mil.-marked tubes (I also note this in my auctions,
but never claim these are any better, only that they passed the mil.
selection). But this usually only means military combed through what the
tube makers sent them to weed out the duds, sometimes this was done
directly by TESLA. Not always, but most of the time, yes.

But some tubes were not sold to public for general use, for example the
TESLA RD25/27*were strictly industrial-grade, and used in transmitters
and/or special large AF amplifiers (the maker, TESLA Vrsovice branch,
made mostly transmitter and high-power tubes, and initially, they
started as part of the British Marconi Company before the
nationalization! Hence the PX25 variants in their program.

TESLA did not build different versions for the military, they tested
regular versions, and if found OK, they gave them mil. insignia
sometimes with date codes and kept them stock until needed or released
them when no longer needed or renewing stock. I once talked to someone
who, when in mandatory military service, worked in one of the stations
that did the testing; and a good friend of mine worked in*1980s in TESLA
quality control (mostly transistors and ICs at that time) and told me
they sometimes did the "crossed swords" stamping etc. for the military
directly, no special tests were made.

For some very special industrial purposes, they (everyone, not only here
but Germany etc.) also tested tubes for example for balanced sections,
noise or microphony, for example for medial instruments like EKG
machines, but the tubes received additional markings after such tests,
military rarely did this.

TESLA made AD1n in several flavors depending on when they made them,
e.g. 1949*tubes are not yet designated "AD1n", just AD1, later*1950s
"AD1n" tubes had some small construction differences, but nothing major.
This is why it is important to also match the tubes for approx. the same
generation/construction..."

[User211]

BTW I don't know what the coloured nipple marking means I have never seen it on Telsa valves before, though I have on Russian OTK.

TBH I doubt the Tesla factory did it.

[andyrlb]

BTW I don't know what the coloured nipple marking means I have never seen it on Telsa valves before, though I have on Russian OTK.

TBH I doubt the Tesla factory did it.

Ok thanks for the information [emoji1303]


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[User211]

Cross swords is the military marking for those who haven't sussed.

[ovlov854]

Hi Andy I have a pair of Red Tips that I used in my Audiomeca for a while and found them to be very good. Since then they are now in reserve as I found a pair of Siemens CCA which I liked even more.
The Red Tips were very detailed without going OTP
No experience of the blue

[andyrlb]

Hi Andy I have a pair of Red Tips that I used in my Audiomeca for a while and found them to be very good. Since then they are now in reserve as I found a pair of Siemens CCA which I liked even more.
The Red Tips were very detailed without going OTP
No experience of the blue

Hi Martin , I initially stuck the blue top in and then 2 days later I tried one of the reds which I’ve now stuck with, I prefer them to the amperex .


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