Spud with filament bias

New idea popped in my head. This will replace the Prologue 2.0 build for now. The new setup just omits the 1626 tube and I can always add that back later. The same transformers and parts will go into this amp.

The idea was to eliminate the cathode bypass cap, so I will hook up the cathode to the heater and add a current source to light up the tube and create a 2V drop for the tube bias. This means the cathode resistor will be so low (3.3R) that it will have next to no effect on the overal output impedance or the LF response.

Mystery of the ДPУ

Might have finally found out what the У(U) stands for in russian tubes that also have the ДP(DR) designation such as the 6Ж49П-ДPУ  and 6Э6П-ДPУ. 

IIRC the max frequency of the standard tubes is 200MHz, but I found a listing from a Ukranian that mentioned the U has the meaning "continuous action gold pins and maximum operating frequency of 600MHz". 

JC's initial guess that these may be suited for UHF seems on the money. As I can't find any kind of datasheet for a DRU type, only DR, it is hard to pin down.

6E5P Test results

© VT52.com


Notice that the µ of this tube is super stable for a high-gm tube. The minimum an maximum for 12 tubes are only 2.7 apart. The twin brother 6E6P shows a spread between 30 and 39. However the gm spread is about twice as large as that of the 6E6P.


6E6P Test results

arm-up time

To get a stable reading, I found out that heating this tube for 20-30s was not enough. The cathode seems to take a long time to heat up and stabilize. After some trial and error I ended up at 10 minutes of pre-heating before setting the tester in action. Luckily the eTracer has a bulk test mode with a warm-up timer you can set.

© VT52.com


Register account

The wonderful world of CMS where the writers of this software thought it funny to handle registration differently than any other software out there.

Sorry for the inconvenience guys, but please register your account again to get access. This time it will ask for your password instead of requiring you to verify your email first and then coming back to set the password.

No wonder it was so quiet here :)