My R390A Feelin' Good Again

[flintstone mop]

Hello
It seems like a almost yearly or every 7 mos thing of getting into this receiver for low sensitivity.
It almost always involves a tube and or alignment. Radio seems to eat 6BZ6's, 1st RF amp. This is the recommended RF amp for a little more ooomph in the front end.

Another PIA is the first rack in the RF deck. Extreme right. There is always some issues aligning the cores so that the rack can move freely while tuning. Any special tricks? That's the first thing I look for is that while switching bands and tuning that the tuning racks move and move freely. There is no old grease involved. Usually a little light application of a silicone on the rollers.

All bands are close to .2 micro volt sensitivity. 7MHZ was almost 5 micro volts. The replacement tube brought that back. The RF amp.

Fred

[WV Hoopie]

Phred,

If the RX seems to eat 6BZ6's, isn't that a clue? I think that receiver uses a 6DC6 as the RF amp? The threads I've read on the R-390/A reflector and "Pearls", most opinions are the 6DC6 can't be beat.

Getting those slugs to move: The holder for each is adjustable! Loosen the screws to center the slug in the core as best as possible. The only item I've seen recommended is talcuum power for the slug & core. Synthetic oil on the racks is gud, maybe 30# on the rollers and 90# where the rack rubs the frame. If there are flat spots on the rollers, you are going to have problems. Purchase gud replacements.

Craig,

[KM1H]

If it eats tubes youre running them out of spec. Use the spec sheet values and they will last a lot longer.

The only place a 390A needs front end help is above 20 MHz and only then when the external noise is well below average. On 40M 5uV is probably OK 99% of the time. What irks me is that you rarely see a thorough test on receiver performance above 20M, its as if the world stops there.

I use a 6GM6 as the ABA (All Purpose Amp); never cared for the 6BZ6 cuz we got all over the map performance out of them and wound up dumping RCA for Sylvania and Telefunken at National.

Personally I think the 6DC6 is a dog ever since I upgraded the 75A4 to a 6GM6 in 65. A 6GM6 really improved a SX-115 also a few years ago and I always use 10M as the benchmark.

Carl

[WV Hoopie]

Phred,

Don't know if you have followed the R-390/A reflector or Pearls, but here is a link to Wei-Li's "Pearls of Wisdom".

http://www.r-390a.net/Pearls/index.htm

There is a section on Tubes, etc., just clickity on the poison of your choice, a pdf file will open. If your Adobe Reader is like mine there is a search feature, type in 6DC6 and read the threads of interest.

At times the quest isn't sensitivity, lower noise is good too.

Craig,

[N8ETQ]

Yeah,


I make sure all those "springy" things are good and straight then
   Find a spot on the MC CHANGE knob where the slugs are all the
way down. Loosen those triangular plates and tighten em right
back up again. Should be gud to go unless you have weak springs
or bent "carrier".

Talcum powder.. Neat.

/Dan

Phred,

Getting those slugs to move: The holder for each is adjustable! Loosen the screws to center the slug in the core as best as possible. The only item I've seen recommended is talcuum power for the slug & core. Synthetic oil on the racks is gud, maybe 30# on the rollers and 90# where the rack rubs the frame. If there are flat spots on the rollers, you are going to have problems. Purchase gud replacements.

Craig,

[KM1H]

Reading those old posts reminded me why I left that list around 97. Lets just say a lot of it wont hold up to peer review but the list gurus were quick at attacking anyone who disagreed with them. The obsessive need to require Orange Drops was another requirement from those clowns. One of those posters now regularly advertises hot rodded souped up 390A's in contrast to his 90's story line; maybe somebody taught him some electronics theory.

As far as sensitivity and tube noise there is a direct relationship. A R-390A is a relative dog for sensitivity at the high frequency end. Its rather obvious just looking at the tubes used and the contract restraints that Collins had with the selections. For its primary use as a military point to point radio it did everything it was supposed to. It is not nor will it ever be the best tube radio for ham use without some rework....never mind the tuning issue. My all Collins 390A is bone stock except for a recap since its rarely used for more than an AM cruiser and mostly on SW BC. Its been around a year since its even been turned on, I much prefer a 51J4 as a general coverage cruiser.

Carl

[flintstone mop]

yea Carl,
I understand that some can get obsessed with different aspects of electronics, even our hobby. Almost like the Audiophools that start dreaming up stories about certain wire passing more frequencies and you have to break it in before you get the advertised performance out of it.
I think there may be some adoration of Collins equipment that it was the cat's meow, but it did what it was supposed to do and it did survive time. It's the pride of ownership to have something that will never be made again. And will survive an EMP event!!!!!!!!!!
Fred