[R-390] Tube Substitutes

[Flowertime01 at wmconnect.com]

Rick,

By 1969 the accessories on the back of R390's were long gone.

By 1975 we could not get the L handle spline wrenches for a TK105 tool kit.
We were using a long handle hex driver with a spline bit installed.

If you have one of those L handle spline wrenches it may be worth more than 
the receiver these days.

The fuses were used up and never replaced if your receiver has clips for 
spare fuses.

Excuse my greenhorn questions, but has anyone tried using 6BH6 tubes in 
the 390 in place of the 6BJ6?  With what results?


The 6BH6 will operate. They will change the noise floor. Us them if you have 
them they are better than not having a working receiver. There are a lot of 
tubes that can be substituted into the receivers. Most of the other stages have 
so much filtering and signal gain over noise that a tube here or their will 
not degrade performance. If you do not get too many odd tubes into the receiver 
it will operate well.

I have not found a wonder tube that just gives a better performance than the 
stock tubes.

Back in 1973 in Okinawa we tried just about every tube we could get. We found 
a lot of tubes would work. Nothing popped up that we wanted to submit the 
paper work on for a suggestion award. We had about 60 technicians and several 
hundred receivers. We were keeping logs and doing serious alignment and signal to 
noise test for comparisons. There was prize money at stake. Most of our 
operators run with manual AGC so sharp and remote cut off pentodes did not cause 
grief. Mostly it was over all signal to noise ratio. Lots of things worked well 
at single signal on the bench with a generator but had lots of noise with a 
real antenna from mixing of many signals in the band pass. 

There is a lot of tubes that will work well. I have never plugged a tube in 
with the correct base match and had the smoke come out.

You need to look under the deck at the actual solder connections. You will 
find that tubes with the screen and cathode tied together may or may not work 
depending on how the tie is made either in the tube or under the deck. You find 
only one pin soldered on the socket and the tube makes up the connection. If 
you get under the deck and make up the other pin, a bunch more tubes can be 
used in the socket.

Fellows have found tubes really very in performance. You may do a signal to 
noise and swap in a different tube type and do a signal to noise and go 
wonderful I found a super new substitute. It turns out you are just comparing a poor 
tube with a different good tube. Once you get two good tubes the difference is 
not there. We find whole batches of good and bad tubes of every type.

Get out the tube manual to look at base diagrams and use what you have where 
you can. 

The quest for the best set of tubes in any receiver never ends. That is part 
of Amateur and Boatanchor Radio.

Roger AI4NI