UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Test Gear and Workshop Equipment

Notices

Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

Closed Thread
 
Thread Tools
Old 21st Oct 2018, 4:58 pm   #1
crackle
Rest in Peace
 
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
Default STC Oscillator 74330B

Hi
Does anyone recognise this Standard Telephones & Cables Oscillator type 74330B.

I would be interested to know what it was used for.
My guess is it would be used for injecting signals into PO private transmission lines for testing, or equipment prior to leaving the factory.
Here are some photos;
Click image for larger version

Name:	STC_74330B_controls.jpg
Views:	170
Size:	74.7 KB
ID:	171282
Click image for larger version

Name:	STC_74330B_detail1.jpg
Views:	165
Size:	91.6 KB
ID:	171283
Click image for larger version

Name:	STC_74330B_detail2.jpg
Views:	146
Size:	65.7 KB
ID:	171284
Click image for larger version

Name:	STC_74330B_detail3.jpg
Views:	147
Size:	114.6 KB
ID:	171285

Larger photos with better details are in the Radio Museum; https://www.radiomuseum.org/r/standa...or_74330b.html

Mike
crackle is offline  
Old 21st Oct 2018, 10:23 pm   #2
Oldcodger
Nonode
 
Join Date: Oct 2014
Location: West Midlands, UK.
Posts: 2,181
Default Re: STC Oscillator 74330B

Mike-my twopence worth, ( more of a semi intelligent hunch)
the frequency range of 300- 2800hz makes me wonder if this was for audio work , as most UK circuits were 300-3.4, all carrier stuff was the same except for early transatlantic stuff which was reduced to 300- 3000.
I'd suggest two options . Telex- something I know little about and perhaps military use as they were not so much interested in the quality of the voice as the accuracy of intelligence of the voice over the line/radio and could work with circuits with the top end being a lot lower than commercial ones.
Oldcodger is offline  
Old 22nd Oct 2018, 6:14 am   #3
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,637
Default Re: STC Oscillator 74330B

Trying to work out the dial which is odd, it starts at 500, goes down to 400, up to 2800, then down (?) finishing at 1400. Also puzzled by it having one valve, if that's the osc valve (L63) then it must have a selenium rectifier but can't see one.

Some nice components but not a very useful bit of kit, Mike.

Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is offline  
Old 22nd Oct 2018, 6:54 am   #4
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
Default Re: STC Oscillator 74330B

There's a finned metal rectifier bang in the middle of the chassis in the fourth picture. It has a centre tap so I assume it's a full wave rectifier's common cathode with a centre tapped mains transformer.

The meter face has the word 'rectified' on it so there must be a small rectifier kicking about somewhere.

It only makes a small number of spot frequencies and only a small number of spot levels (the meter has only a reference mark, not a graduated scale) The gap in the frequency coverage says ir's for checking the upper and lower roll-off points of some audio path.

Some radio systems don't go above 3kHz. It doesn't have to be for wired phone systems.

A very application-specific tester!

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Old 22nd Oct 2018, 7:02 am   #5
crackle
Rest in Peace
 
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
Default Re: STC Oscillator 74330B

Hi Andy
The selenium rectifier is visible in the last photo.
The left hand knob, which is marked "P.S." has the following settings;
300 400 500 800 1400 1600 1800 2000 2200 2400 2600 2800. It isnt clear but I am assuming this is marked in cycles per second or Hz.
The right hand knob is marked "D.B. Send" and is calibrated in.
-30 -20 -10 0 +10.
The 2 black thumb screw terminals top right are marked with AC symbol "~" I would assume this the output.
The black knob under these terminals is just a handle for lifting as is the black knob opposite on the left under the earth terminal.
The black thumb screw terminal top left is marked with earth symbol.
The centre knob at the bottom is marked "OSC"
The 2 fuse carriers are marked "0.25 Amp" they are very nicely made and slide down before lifting off, they have standard type fuse wire fitted between the terminals.
There does not appear to be any other cable entry points and the insides to me look complete.
I am almost tempted to run it up on the lamp limiter and variac.
I imagine the centre calibrated meter is used to set a prescribed level.
I forgot to say there is a 50's style electrolytic fitted, which looks to be a replacement.

I have been wondering about the year of manufacture. The capacitors look like paper in wax/bitumen types encased in a metal can. Similar to those used in late 20's to mid 30's radios. The resistor immediately to the right of the valve in photo 2 is one of those with fuzzy colour bands as if they have been spayed on. There is the dog bone resistor on the right. There is a black moulded mica capacitor just behind and to the right of the dual ganged pot.

Keep the comments and ideas coming.

Mike

my reply crossed over with David's

Last edited by crackle; 22nd Oct 2018 at 7:18 am.
crackle is offline  
Old 22nd Oct 2018, 11:07 am   #6
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
Default Re: STC Oscillator 74330B

I'm still staggered by the number of nuts on the fuseholder connections!

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

Last edited by AC/HL; 22nd Oct 2018 at 12:05 pm. Reason: Forum rules
Radio Wrangler is offline  
Old 22nd Oct 2018, 4:07 pm   #7
crackle
Rest in Peace
 
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
Default Re: STC Oscillator 74330B

I gave it a try, and it works, I first disconnected the very leaky HT electrolytic and a 250uF 12v one which I believed was in the cathode circuit across a 300 ohm resistor, and tacked in some temporary replacements.
It worked OK giving about 3v output with no load, and about 1.3v into 600 ohms.
But it has a strange HT supply, I believe it is a voltage doubler as the transformer HT winding is only 90v. There was about 150v on the final HT.
The dual variable resistor does set the level, which is slightly short of the set point on the higher frequencies.

Mike
crackle is offline  
Old 22nd Oct 2018, 10:21 pm   #8
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
Default Re: STC Oscillator 74330B

There is some similarity to this one:

https://www.gracesguide.co.uk/images...7-STC29a-1.jpg

Lawrence.
ms660 is offline  
Old 22nd Oct 2018, 10:35 pm   #9
crackle
Rest in Peace
 
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
Default Re: STC Oscillator 74330B

Well done Lawrence for finding that, it is almost the same, slightly higher frequency, now where is the instruction manual and circuit.

thanks
Mike
crackle is offline  
Old 23rd Oct 2018, 5:35 am   #10
Diabolical Artificer
Dekatron
 
Diabolical Artificer's Avatar
 
Join Date: Jul 2009
Location: Sleaford, Lincs. UK.
Posts: 7,637
Default Re: STC Oscillator 74330B

Ah, spotted the rectifier, I thought it was a coil of wire, think I might need new glasses.

"I have been wondering about the year of manufacture." Looks late 50's maybe early 60's Mike, though I'm no expert.

Andy.
__________________
Curiosity hasn't killed this cat...so far.
Diabolical Artificer is offline  
Old 23rd Oct 2018, 8:55 am   #11
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,800
Default Re: STC Oscillator 74330B

Most of those bits were available in the late thirties, but telecomms stuff always was built older style than the actual date!

Middle fifties would have seen PVC insulated wire.

It doesn't seem to suffer from wartime economies. 1950?

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 8:57 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.