Hunts CRB3

[Alistair D]

I have updated the schematic to show the changes. Again I am only showing a clip at the mo. Full schematic will follow when we are all happy that it is correct.

I am keeping an eye on possible production changes and will try to incorporate them.

Once again, thanks to everyone that has contributed.

Al

[OldTechFan96]

Here is a rough resistor placement chart. Note the three resistors under the main potentiometer that are not in the Hunts circuit.

The adhesive that holds together the base of the neon indicator and the EM34 has failed. Probably worth others checking theirs.

[Chris55000]

Hi!

Member OldTechFan96, could you tell me the colour–bands on the three ¼W carbon comp. resistors under R4 please? – I can read one at 47R, but the others aren't clear!

Did the Colvern Pot R4 actually have a tap on it as well as the wiper and end–tags, or was the tag where (what appears to be) the 6R8 and R3 is connected, the CCW end of R4?

For completeness, can anyone measure the d.c. resistance between the CCW end of the Colvern Pot and it's tap please so I can correctly annotate my diagram please?

Chris Williams

[Chris55000]

Hi!

Originally Posted by Alistair D

Chris, No need to create another schematic.

Oh dear! I've just been putting the finishing touches to my diagram before you posted this!

Chris Williams

[Chris55000]

Hi!

Hunts CRB3 Circuit Diagram, Version 1!

Chris Williams

[M0FYA Andy]

That circuit is very impressively redrawn! Well done!

Andy

[OldTechFan96]

Morning Chris,

The three resistors under R4, from left to right, are:

Brown, green, black, gold

Yellow, purple, black, silver

Blue, black, gold

The Colvern pot at R4 does have a tap at 2:00. R3 is connected between the RHS track and the tap.

What is 'CCW'?

If anybody wants the 4K original photographs of the CRB3 please send a PM!

[ms660]

Just a thought on a point I made earlier, there's no direct connection between R8 etc and R4 in any of the CRB's looked at so far that I can see.....?

The resistor(s) that are fitted to one or both ends of R4 are "trimming" resistances selected to suit the pot so far as I can make out...?

Lawrence.

[m0cemdave]

Thanks for that, nice work!
I was going to do something similar when I finished my rebuild, so it has saved me a job.
I'll try to proof read it for you, after printing it out. For some reason I've never been able to proof read from a screen...

re the previous question:
CCW and CW on a circuit diagram indicate the direction of rotation of pots and switches. Counterclockwise and Clockwise respectively.

[Alistair D]

Chris, I can see at least three occasions where you have copied directly from my drawing and then added your own name to it. I find that very underhanded and unfriendly way to treat a fellow member. What also annoys me is that not long ago I helped you out by emailing a copy of a very rare manual.

Nuff said

Al

[Chris55000]

Originally Posted by Alistair D

Chris, I can see at least three occasions where you have copied directly from my drawing and then added your own name to it. I find that very underhanded and unfriendly way to treat a fellow member. What also annoys me is that not long ago I helped you out by emailing a copy of a very rare manual.

Nuff said

Al

Hi!

I feel that's a bit unfair – the values I got were provided by Lawrence in his list and the circuit symbols, diagram layout, template layout, etc., were entirely of my own design using my Abacom software!

My component symbols were measured and drawn from the list of symbols given in "Beginners Guide to Radio", "Practical Wireless Service Manual", etc., for the old style ones, and a Thorn Service Manual for newer ones and semiconductor devices.

The lettering came from Chris Flippard who very generously emailed me his permission to share it on here!

From forty years of reading British Technical magazines I learnt the accepted ways of drawing sections of circuits so as to make them the clearest to read and understand, and rest assured any sections of my drawing that look like yours (or anybody else may draw) is entirely coincidence!

The symbol for the EM34 indicator, for example, is a standard one used in P.W., P.T., W.W., etc., everybody shows the valve this way, altho' it's not very common to show the target–anode as an open rectangle – this is a convention recommended by BS 530 to indicate a fluorescent screen or target!

If my diagram looks like a direct copy from.anything you provided it is purely coincidental, and I apologise, and the layout was drawn/rearranged by me solely from my desire to make it as clear to read as possible!

Chris Williams

PS!

I don't possess a CRB3 but if I had and nobody else had uploaded a schematic, rest assured the result would have been the same!

[m0cemdave]

I have the following notes / corrections, having studied the wiring on my unit. Hopefully somebody else will be able to check another one and confirm, or amend further accordingly.

R1 = 1k2, 2W

R3 goes directly to the CCW end of the pot, i.e the other end of R4A
R4A is a wire link on my unit

add R4B at the CW end of the pot, it's 150 ohm 0.5W on my unit
(so R4A and R4B are presumably AOT trimmers, as suggested above)

R4 pot value is 5k, not 1k

R14 = 10k
R19 = 6k8
(i.e the values are transposed)

My transformer is labelled 425V 40mA, not 20mA

and yes, R8 and R4 (via R4B) are connected together

HTH

[Chris55000]

Hi!

Thanks for the updates – I realised I'd annotated the value of the Null Balance pot R4 as "1k" in error after I'd uploaded it!

Not having a CRB3 myself the figure of "20mA" for the current rating of the h.t secondary (and the other two windings) was estimated from existing published designs in the Magazines – are the other two windings annotated with their rating on the actual transformer?

Chris Williams

[ms660]

Already pointed it out twice before about the connections observed regarding connection of R8 etc to R4, anyways here's a drawing I done using my latest drawing software to show what's what so far as I can make out.

Lawrence.

[m0cemdave]

The other two windings are annotated and are per your drawing.
Lawrence's drawing is correct, makes it nice and clear too (but don't forget R1).

[ms660]

I left the tag "R1" out on purpose on the schematic because in some units it might not be fitted, if I was to draw the whole schematic however, I would ditch R4 for VR1 and R8 for VR2 and use my own numbering for the rest of the resistances with the two "R4" compensating resistances (when fitted) being given the ref R1* and R2* with a ref to * being given on the schematic somewhere.

Lawrence.

[Chris55000]

Hi!

Amended Diagram uploaded in light of Member's updates & corrections!

Chris Williams

[m0cemdave]

Chris:

You still need to move the lower end of R3 to the junction of R4 and R4a. It's wired directly to the pot terminal, then the terminal is wired elsewhere via R4a (which is a wire link on my unit).

And R1, at least on my unit, is 1k2 (i.e. the same as R2)

HTH

[Chris55000]

Hi!

I think I've covered all the eventualities & permutations now!

Chris Williams

[ms660]

Also SW1R should be SW1F and SW1F should be SW1R, also I would indicate that the minium resistance for R4a & R4b as 0 ohms, lowest value resistor fitted that I have found is 3 Ohms so far as I can make out from the band colours:

https://www.vintage-radio.net/forum/...3&d=1448461941

I would question the presence of R1 as such.

Lawrence.