The "Sussex" Homebrew Valve Tester.

[Mike Brett]

Hi Martin
Thanks for the information. I found out that Maplins sold single .6 watt resistors but at 32p each that is a high price to pay even by Maplins standards.
Mike

[Mike Brett]

Hi all
The last BOM states that caps C4, C5, and C6 6.8 nf were too fat for the PCB.
In post 240 Mike said 10n or 4n7 would be suitable. Can anyone tell me what was eventually used, and is there an order code for these.
Cheers Mike

[Top Cap]

Mike it was some time ago but I believe the pitch for mounting is 5mm?
If that is the case, Cricklewood do some suitable CODE CPB6n8

http://www.cricklewoodelectronics.co...=search&page=1

[Mike Brett]

Many thanks for that TOP CAP, when I get the PCB I will check the pitch and order some.
Cheers Mike

[Mike Brett]

Hi all
Some constructors of the Sussex VT1 have included an extra meter to indicate heater voltage. I would like to do this also, just as a visual reassurance that all is well. As I understand it the simplest way for me would be to run the meter from a small transformer on AC. I assume the meter drive would be connected across the heater terminals, not sure precisely where though, is it that simple?

Mike

[Ed_Dinning]

Hi Mike, if you use the same style of meter it would be possible to wind 19 turns of thin insulated wire between the winding and the core. This will give you a supply for the additional meter. You could also use an AC moving coil meter as loading is not an issue on the heater circuit.

Ed

[Mike Brett]

Hi Ed
Yes I intend to use a meter to match the others, so I will go with your idea, saves the price of another transformer.
Cheers Mike

[Mike Brett]

I am gathering the valve sockets together for my Sussex build and at present I have the following.
British nine pin B9.
British seven pine B7.
B9G.
International Octal AO8.
Mazda Octal MO8.
B7G.
B9A.
8A.
I have chosen these simply because they are the valves I have in my equipment at present. I believe the AVO tester has 22 types, so my question is this. Without making my tester to complicated is there any base type that is not in the above that is common
and I am likely to regret not fitting it. Difficult I know to answer but it would be easier to add to the list before I start building.
Cheers Mike

[Meat Pye]

Sounds like you have most bases covered there (no pun intended) with that line up. If you ever need to accommodate US, side contact, B5 valves etc. then best to make a breakout box with the extra sockets wired to a B9A/B9G plug which would avoid cluttering your Sussex with rarely used sockets.

[Mike Brett]

I found the attached extension lead and plug in my junk box. The plugs are only 8 pins, but that should be okay for the American valve bases, I think. The only other problem I can see is the wires in the cable may be a little bit too thin, so I might have to change this for a thicker cable.

Mike.

[Ed_Dinning]

Hi Mike, that adapter looks as if it will do nicely. You had certainly left out an important one, the B4 / 5, lots of valves with those bases. Ct is useful. That covers most of the common ones.
If you will work with US valves then UX 4,5,6,7 are useful.

Be careful using the adapter with high gain valves as you may get instability.

Ed

[Mike Brett]

Thanks for the info Ed. I have room for one more base so I will add the B4/5 to the Sussex top panel. That gives me nine bases plus the 8 pin socket for the extension lead. I might get away with the lead as it is. It has two thicker wires I can use for the heater, the rest are a bit thinner, I will have to see how it goes.
Mike

[Ed_Dinning]

Hi Gents, a further thought for extensions. It is possible to buy quite cheaply, an 11 pin octal style relay base that is used with 3P c/o relays. Get a dead relay and you have a very useful 11 way extension lead for different valve bases etc.

Ed

[mikeydee]

I am still debugging my sussex build.

I did have some problems that a few people had suggested were linked to parasitic oscillation but actually in debugging that issue I found a bad solder connection on my selector switches which I think was the cause. During that debugging I have disconnected all the sockets except the octal one and fitted ferrite beads both at the selectors and on the socket end too so hoping that can rule out oscillations.

I have two questions/issues that I would appreciate some help with right now.

1. Just to confirm RL1's job is to isolate the HT, right? But on my build I have the HT light on all the time and accompanying voltage. That can't be right can it? However when I look at the PCB tracks and the circuit it looks like the HT can follow the wire link to the middle pins of the relay (11/21) and also go straight to D3 and R1. Is there some tracks to cut that I have missed perhaps?

2. Apart from that the tester largely seems to be working except that the GM measurements are very low e.g. 0.5 on several EL34 although they work fine when used in an amp.

Any thoughts much appreciated.
Mike

[G8UWM-MildMartin]

I've just had a look at the PCB tracking and circuit and confirm your findings of the discrepancy around RL1.
Probably easiest to cut the track between the RH link and C2 then join C2's top end to the top track or the top end of the fuseholder (if fitted).
Wish I'd spotted that!
Best regards,
Martin

[mikeydee]

Hi Martin, I am really relieved to hear that you get my point. surely many others have used the PCB so they would have seen the issue before, if it exists

let's see what others say.

[Mike Brett]

Hi Mike
I am just in the process of populating my board so have not had the chance to test it yet.
I can see what you mean by the direct connection to D3 and R1. If this is really an issue I agree that it is very strange it has not come to light before. If you have or do intend to cut and rejoin the track could you let me know how you get on, then I will try the same prior to fitting my board.
Cheers Mike

[mikeydee]

Ok, so I have cut the track between +ve end of C2 and the wire link, then bridged C2 +ve end to the top track which is connected to the fuse as per Martin's suggestion.

This was required otherwise the HT would be there all the time which would presumably upset the leak tests. Also I noticed quite a loud arcing from my test switch when returning to the Leak 2 position.

Fixing the HT has impacted my test results positively but I am not certain that that I have resolved all issues as the GM is much lower than the spec figure of GM=11 and Ia=75mA.

new JJ EL34 GM=5.5 Ia=75mA
new JJ EL34 GM=6.9 Ia=71mA
old unknown EL34 GM=1.9 Ia=87mA

Any thoughts?

PS I wonder is there anyone near me in Bristol that I could compare readings with?

[Mike Brett]

Hi
Can somebody tell me please if the 22 uf 400 volt capacitor C13 is an electrolytic.
Cheers Mike

[mikeydee]

C13 is an electrolytic in my Sussex.