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-   -   807 vs. 1624 tetrode ? (

coresta 4th April 2006 08:57 AM

807 vs. 1624 tetrode ?
Hi Tubholics ! :) I 'm working on project of 807 PP amp or even PPP as i have 50 NOS on hand . But when i see the 80 1624 i have too, i'm asking myself if DHTetrode wouldn't a better choice ? (even if an additional DC 2,5v PSU will be necessary ) Did someone here have a listening test on these bottles ?:rolleyes: Cheers

Giaime 4th April 2006 10:53 AM

Well, if you have so many you could send a couple to me to evaluate their sonic possibilities :D

SHiFTY 4th April 2006 07:47 PM

807 is identical to 1624 apart from sockets and 2.5V 2A heater. (might be directly heated? Should be able to see if it is.)

Just build a really good design, and you can use either. I would sell the 807s to fund the project and use the 1624 instead, seeing you have so many!

I built an 807 PP amp with a 550V B+ and it sounded very good.

coresta 4th April 2006 08:15 PM

Hi Shifty and Giaime, yes the 1624 is DIRECTLY heated to instantaneously recover the transmitting function in mobile transceivers . I am selling some pairs on because of ... so many tubes, so little time :D I 've had 6l6 PP amps and was very happy with them , especially on VR screen PSU ; no more ULTRALINEAR :xeye: Cheers

Giaime 4th April 2006 09:02 PM

You're saying that you liked 6L6 in pentode mode with screen regulation instead of ultralinear?

That's interesting.

Also because 6L6 was invented BEFORE ultralinear ;)

Miles Prower 5th April 2006 01:39 AM


Originally posted by coresta
I 've had 6l6 PP amps and was very happy with them , especially on VR screen PSU ; no more ULTRALINEAR :xeye: Cheers
I did an 807 amp that way: screen regulation and local feedback. That worked out very well indeed: sounds great. 807s aren't really very well suited to ultralinear anyway.

coresta 5th April 2006 06:23 AM

yep! for sure : have a look at the Western Electric amps with 350B : Hafler Keroes were at school at this time ;) And 350B was the king in movies :D

Shoog 5th April 2006 06:18 PM

Why aren't 807's well suited to UL?. I would have thought that there lower than normal screen current would have made them more suited. I am currently running my Parafeed 807 SET in UL at 350V and like it as much as in triode.


coresta 5th April 2006 06:25 PM

Hi Shoog, it's a tetrode, not a pentode . The space charge do not respond to the same law .. But the main reason is that UL was intended to "improve" the linearity of existing toobz , its an Xformers patent , not a tube development . :)

rcavictim 5th April 2006 06:32 PM


The max screen voltage on the 807 is quite low at just 300 volts, 100 or more volts lower than 6L6, 6CA7, 6550, KT88 etc.) so one cannot easily enjoy a UL circuit that takes advantage of the high plate voltage capability of around 750 volts on the 807. This is the same reason many otherwise attractive TV sweep tubes are no good for UL. Many of those have a screen designed for max 150-175 volts.

An output xfmer with a separate screen winding is all that is needed to overcome this easily but it comes at great expense. There are voltage dropping techniques that can be applied between the UL screen tap on the xfmer and the screens, like VR tubes, etc., but their application is relatively unknown and the experience pool tiny.

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