[AMRadio] R-390A Help


W2XJ w2xj at w2xj.net
Tue Jul 8 22:18:00 EDT 2014


I agree that a resistor is an adequate replacement for the 3TF7 but they didn't go to all that effort  for nothing. This probably is a way to mange oscillator noise since they put the VFO and BFO filaments in series and added filtering and an expensive short lived ballast tube. I am not sure what that buys for typical day to day use but it was done for a reason. In the spirit of keeping the unit as original as possible, I would solid state it. Others have suggested taking the two oscillator tube filaments from a series to parallel configuration and just feed 6.3 volts like all the other tubes. 

Sent from my iPad

> On Jul 8, 2014, at 1:28 PM, rbethman <rbethman at comcast.net> wrote:
> 
> I'd add that there is NO reason to buy a 3TF7 ballast tube.
> 
> A simple and inexpensive 49 - 50 ohm 10W resistor across the two pins the 3TF7 uses is all it takes!
> 
> Ran a '67 EAC that way for about 6 years.  Not a single problem. I do happen to have a 3TF7, but I'm going to just hang on to it. I also have a handful of the 26Z5Ws.  I worry less about solid stating them than I would worry about that selenium rectifier.
> 
> When the selenium rectifier goes, you definitely do NOT want to get a nose full!  It is a nasty gas that they let go of!  Not good for the human body.
> 
> The two can caps can be gotten from Tom N0JMY at hayseed hamfest. They make them from the ground up all new.
> 
> Re-stuffing them is a pain that only gives you the "satisfaction" of making it "appear" to be original.  Not worth the work and effort.
> 
> Make sure all the capacitors are up to snuff!  Usually better to re-cap if it isn't an EAC.
> 
> Almost all the rest are too old and have the Brown Beauties, referred to as BBOD, (Brown Beauties of Death).
> 
> Make darn sure that the DC blocking cap on the filters is rated for 1 or more KV.  You don't want to be blowing filters!
> 
> Filters are getting as rare as hen's teeth!
> 
> Bob - N0DGN
> 
> 
> 
>> On 7/8/2014 12:43 PM, W2xj wrote:
>> You should really download an on line version as some have more detail and background information.
>> 
>> I should note that every single tube in that radio can still be bought as old stock never used online.
>> 
>> These guys have everything but the ballast tube which can be had from fair radio
>> 
>> http://www.vacuumtubes.net/prices.htm
>> 
>> Rectifiers are $20 each and the ballast is $60 while the other tubes are between $3&$7. That is a good reason to go solid state on those three expensive tubes.
>> 
>> Sent from my iPhone
>> 
>>> On Jul 8, 2014, at 11:51 AM, Bill Guyger via AMRadio <amradio at mailman.qth.net> wrote:
>>> 
>>> Thanks to all that replied, now to go diggin'! Just wanted to see if any of you had any hot sports opinions before I go hunting.  Shouldn't be a real chore once I get time, a manual was included along with the radio.
>>> 
>>> Tnx 73 Bill AD5OL
> 
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