Racal RA7915 main receiver board schematic needed

[John Crighton]

Does that apply to the TRA7928/38 transceivers as well? It's a long time since
I've looked inside them - although I have a working '38A stowed in the garage.

Hello Budgie,
yes all those bad things apply to your oven oscillators too.
Write yourself a little note saying
"Warning unsolder oven thermistor before removing casting"
and slip it inside the set. If your clarifier switch/pot has an
orange coloured plastic switch then change it.
10K ( A linear) with dual switch.
I changed so many pots, I still remember the value. Heh heh heh....
The switches on the back of the pot are unreliable.
Maybe they go bad because they don't switch much
current. Don't know. Anyway, they give problems by not
switching from AM to SSB reliably.

Budgie, you have your finger on the pulse regarding
spare parts and where to get them.
I am looking for a couple of ICs
SL1621C and NE571N (SA571N)
Farnell have the SA571N but not the SL1621C
I would like to buy them at the same place to save
postage. No luck at RS for either of them.
Any ideas?

Regards,
John Crighton
Sydney

 

[John Crighton]

**** John,many thanks for your efforts.A large dollop of luck saw me
pick up a cheap single channel 7915 over the weekend,and,yes,it is
fitted with the USB filter!!!

Regards,Brian Goldsmith.

Lucky You! Great stuff!
If you have an ordinary RF sig gen, you can disconnect the
channel oscillator coax at say the main board and use your
sig gen as a channel oscillator (10.7 Mhz above your desired
channel) and have a play around as though the set had
variable tuning, 2 to 12 Mhz ( was it 10 or 12? I can't remember.)

A posh sig gen with digital readout is great for this purpose.
That is what I liked about these old Racal transceivers and
receivers such as yours. Was it an ebay purchase?

Regards,
John Crighton
Sydney

 

[John Crighton]

Hi John,
The Oven unit is next on the list for a look at. I'll be checking all the
resistors, including the one you mention.
I'm going to do the mod to widen the freq range of the clarifier into a BFO,
I see there is a cap that changes value if clarifier or BFO mode is wanted.
Another thing, I might disable the heater, to see if the xtals are stable at
room temp. Ive read this was a common mod that was done to these sets?
JEFF

Disabling the heater is not as bad as it sounds, Jeff.
For us hobbyists, quite a good idea reliability wise, just means
you will have to adjust the little trimmers and maybe change the
little fixed capacitor associated with the trimmers for each channel
xtal as well as the 10.7Mhz carrier insertion oscillator.

I was just mentioning to Brian that you can use a signal
generator 12.7Mhz to 22.7 Mhz to replace the fixed xtal
channel oscillator to make your receiver continuously
tunable from 2 to 12 Mhz. Just for fun.

Regards,
John Crighton
Hornsby

 

[budgie]

Hello Budgie,
yes all those bad things apply to your oven oscillators too.
Write yourself a little note saying
"Warning unsolder oven thermistor before removing casting"
and slip it inside the set. If your clarifier switch/pot has an
orange coloured plastic switch then change it.
10K ( A linear) with dual switch.
I changed so many pots, I still remember the value. Heh heh heh....
The switches on the back of the pot are unreliable.
Maybe they go bad because they don't switch much
current. Don't know. Anyway, they give problems by not
switching from AM to SSB reliably.

OK John noted all above for the next time I get THAT deep into the garage ...

Budgie, you have your finger on the pulse regarding
spare parts and where to get them.
I am looking for a couple of ICs
SL1621C and NE571N (SA571N)
Farnell have the SA571N but not the SL1621C
I would like to buy them at the same place to save
postage. No luck at RS for either of them.
Any ideas?

Thanks for the glowing compliment, but I don't have any leads on the 1621. Is
that a Plessey chup?

 

[Brian Goldsmith]

"budgie" wrote

Is that a Plessey chup?

**** Nah,you wont find those chups with your fush down at Brudge Road
,Ruchmond at half past sux!!!



Brian Goldsmith

 

[Jeff]

John, both are listed here... are you rich?
ne571
http://www.jabdog.com/semi-lin5.htm
sl1621
http://www.jabdog.com/semi-lin6.htm

JEFF

 

[budgie]

"budgie" wrote

Is that a Plessey chup?

**** Nah,you wont find those chups with your fush down at Brudge Road
,Ruchmond at half past sux!!!

FWIW we have a real live actual working F&C shop in Subiaco (WA, not Italy)
whose sign says "Fush & Chups".

 

[John Crighton]

Thanks for the glowing compliment, but I don't have any leads on the 1621. Is
that a Plessey chup?

Yes it is Plessey chup. Heh heh heh.....
Thanks anyway,
John Crighton
Hornsby

 

[John Crighton]

John, both are listed here... are you rich?
ne571
http://www.jabdog.com/semi-lin5.htm
sl1621
http://www.jabdog.com/semi-lin6.htm

JEFF

Cripes that SL 1621 is expensive.
Thanks for your efforts there Jeff.
Regards,
John Crighton
Sydney

 

[felix_on6be]

RA7915

Hi all,

Answering now to an orginal very old thread but hoping finding back above discussion participants...

I just got 2 pcs RACAL, fixed channel (6) communication receivers RA7915.

They appear to be made bij RACAL Sydney Austr. branch and have the very early serial no's 16 and 19.

I found pics and even a manual on the internet but apparently the versions I have seem to be much older as the one described in the manual. For example, I see hughe differences in the oven oscillator type 2723.

The sets are incomplete, one has a complete board missing and both are badly mistreated in the oven oscillator. Especially in the oven electrical circuit the manual describes extensive control systems with IC's, my version has simple transistors only.

Though I guess I could make a complete set out of the two pcs.
I think they originate from the Belgian Maritime coastal station.

Anyone there that has more information or a schematic on the more older serialno.'s? I need especially data on the oven oscillator 2723 since these are really in a bad condition.

If you have some more info on these more early version, please let me know.
Links to newer docs are included in my other post in "Datasheets,Schematics, Manuals and parts section of this forum.
For some reason I am not allowed to repeat them here.


Kind regards
73's
from Felix, on6be