Hunts CRB3
 

Collecting my CRB3 is obviously on hold at the moment. In the meantime I have been tidying up a copy of the schematic. The next part of the process is to add component values. I did find a drawing that that had them added but many of the values measured rather than standard.

Does anyone have a components parts list that I could have?

I will post the completed diagram for everyone to use.

I may also have one two extra questions that need clarifying.

Al

Re: Hunts CRB3 parts list
 

I have this annotated circuit diagram.

Re: Hunts CRB3 parts list
 

if it uploads the info is on the forum 2017

Re: Hunts CRB3 parts list
 

that may be the wrong photo

Re: Hunts CRB3 parts list
 

Thanks chaps. Alas both of those drawings are for an earlier model.

I have attached an untouched copy of the CRB3 schematic.

Al

Re: Hunts CRB3 parts list
 

Hi!

If anyone who's got a CRB3 can email me high Res photos of the internals I can marry up the components with the diagram and redraw it!

I tried getting one myself but some clot bid over £400 for it and no EM34 in it either – it had been substituted with a 1629 12.6V eye out of surplus somewhere!

Chris Williams

Re: Hunts CRB3 parts list
 

I have an early CBR3, serial number 147, if anybody would like pictures and part references etc.

Re: Hunts CRB3 parts list
 

Oldtechfan, how easy would it be for you put values beside each component reference?

Al

Re: Hunts CRB3 parts list
 

Hi,
I do have one of these, but can't get to it because of lockdown related things..
It is going to need repairing and re capping at some point...
Any additional info would be most useful. they are deceptively simple I think.

Re: Hunts CRB3 parts list
 

No problem! Will get it done today!

Re: Hunts CRB3 parts list
 

As far as I can determine, the most comprehensively updated circuit is that by forum member Ron Bryan, dated 13 November 2017.

It's attached here it it's any help.

(I don't have a CBR3).

Re: Hunts CRB3 parts list
 

Alistair's diagram is the one.

Some pictures from a CRB3 undergoing refurbishment:

Re: Hunts CRB3 parts list
 

and some more:

A few component values:
R1 = 150 ohms
R3 = 500 ohms 1% hi-stab
R11, R12 = 1M
R3 = 4M7

Re: Hunts CRB3 parts list
 

I tried to edit the above post but it timed out, here is the updated text:

and some more:

A few component values:

To large pot:
R1 = 150 ohms 0.5W
R3 = 500 ohms 1% hi-stab

Around magic eye valveholder:
R11, R12 = 1M
R3 = 4M7
1x 0.01uF 1000V

On large tag board:
2x 1k2 3W
1x 10k 3W
5x 68k 3W
1x 200pf 1% SM
1x 0.02uF 1% SM
1x 2uF 250V MKA

On small tag board:
1x 50 ohms 1% hi-stab
1x 5k 1% hi-stab
1x 500k 1% hi-stab
1x 68k 3W
1x 33k 3W
1x 27k 3W
1x 0.47uF 250F

The 3W types were originally carbon, probably 2W rating

On switch:
2k2 3W Welwyn wirewound

Large pot (measurement):
Colvern CLR 6040/13 5000 ohms G
Small pot (power factor):
Colvern CLR 5001/11 1000 ohms

PSU capacitor = 16 + 16 uf, 500V

The Selenium rectifier will be replaced with a 1N5407 plus series resistor,value to be determined.
The flying mains lead has been replaced with an IEC socket, the panel and chassis being punched accordingly.

Re: Hunts CRB3 parts list
 

All gratefully received.

I don't want to post the whole diagram yet as it is incomplete. I have attached a snippet to show what the finished article should look like.

Al

Re: Hunts CRB3 parts list
 

Alistair - I have just removed the reference to C6 on the valveholder, it may be C4 ! Apologies...

Re: Hunts CRB3 parts list
 

Thanks Dave - I see that the circuit I posted was for the 1945 version whereas the one under discussion is the 1953 version.

Quite a comprehensive Operating Manual, which includes the circuit, as in Alistair's post, with the blue Biro cross on the switch wafer with C4 above. (Not sure what that's intended to indicate). Rather a pity that Hunts didn't annotate the component values and tolerances on the circuit, but that said, I guess that anyone restoring a CRB3 can see the values marked on the existing components anyway.

An expensive instrument in its day no doubt, and an interesting piece of Test Gear 'archaeology', worthy of restoration.

Re: Hunts CRB3 parts list
 

Dave, re your comment "The Selenium rectifier will be replaced with a 1N5407 plus series resistor,value to be determined" in post #14.

The marked up diagram I referred showed an extra resistor in series with the rectifier as shown in the attachment. The value was marked as 1k4. The fact that it was a measured value makes me think that it was an original fitment. Perhaps it is only in later or earlier versions.

Al

Re: Hunts CRB3 parts list
 

Thanks Alistair, I will use that as a starting point when I put it back together.

And thanks to David for the full manual.

Re: Hunts CRB3 parts list
 

Hi!

If you fit 5 X 68k resistors on the large tag board, you'll not get the magic–eye to light if they're R14 to R18 as I suspect them to be!

A picture I found on Google "images search" shows them clearly identified with a RED spot using the obsolete "body–tip–spot" coding, hence 6k8 2W!

I am draughting a new "Newnes quality" circuit diagram from Hunt's ghastly mess and it should be ready 2mrw afternoon!

Chris Williams