The "Sussex" Homebrew Valve Tester.

[ColinTheAmpMan1]

Hi,
I have made an enquiry to EECO regarding thumbwheel switches. They have what might be a good option for the pin-selector switch. The part number is 9R177601G and it is a sizeable nine-station switch which should take the 3A current and 350 V, if non-switching. The spec sheet is attached. The thing is, they quote £84 (plus a small p+p charge) for each switch, just so long as I order three minimum units. Otherwise, there is an small lot charge of £74, which is close to the price for one switch! Would there be any interest in the extra switches by anyone else?
Regards, Colin.

[ColinTheAmpMan1]

Hi Folks,
I thought I would try to check my DPMs from "Daifengsu" before using them (and leaving positive feedback). While the 200 VDC and 200 mVDC don't present much difficulty, the 200 mVAC required a signal generator and oscilloscope to get anything like the right ball-park. A Fluke 175 didn't even seem to be agreeing with the DPM and oscilloscope, even though the AC voltage range is quoted down to 30 mV. Has anyone else tried this and had similar results?
Colin.

[ColinTheAmpMan1]

Hi,
Further to my last post and with reference to an earlier post that I made in respect of the linearity of the DPMs, I have done a bit more investigating.
I used a sine-wave generator giving 999.6 Hz and checked the 199.9 mV AC meter against my Fluke 175 to get these figures:

Fluke 175 DPM
197.5 199.9
176.2 190.6
140.7 170.2
118.3 150.7
86.0 110.3
77.9 100.1
76.4 98.1
58.7 75.2
54.5 69.8
39.2 50.2
23.6 30.1
15.8 20.0
7.9 9.9
4.2 5.1

Changing to 50 Hz gave slightly better agreement. The DPM was purchased from "Daifengsu" and is one of two. The other shows similar results. Some of these strike me as rather alarming. If the error is unimportant then why are Gm figures quoted to one place of decimals?
I should probably state that while my Fluke 175 is not currently in calibration, it agrees with my 'scope (also uncalibrated) to within a few percent.
I think I might buy another from "Giorgio" to see if it is any better.
Regards, Colin.

[Refugee]

I read this thread with great interest and am impressed with all the home brew design engineers we have.
On looking through and having a quick check of the RAT it looks reasonable to use a SMPSU for the heater. This would allow for the voltage to be switched and also have a fine tuner at low current dealing with the issue of switch ratings and allowing low emission to be checked by reducing the heater volts by say 20%.
The main trouble is that a lot of my valve stuff had to go about 3 years ago so I don't have enough valves to test but could have a look at any tester that can be brought to me in the East Midlands as long as it has enough heater power to do octal valves with there 2 amp heaters.
You can have a look at the Bell and Howell I fixed. It is in success stories to see the valves I am talking about.

[REAGANS]

Hi,

I have been reading through this thread since January and have now sourced most components to build the "SUSSEX", but now need to get a transformer.

I've seen post 656 from Ed Dinning regarding winding transformers but I do not know how to contact him. Great project and there appears to be many building the tester.

[oldticktock]

Click on Ed's forum name and you will see the option to PM him .

Chris

[REAGANS]

Thanks, have done, think I may have got the last one.

[buglegirl]

Hiya,

Kinda been lurking here for a while. I am based out of the US and I am wondering if the PCB's or Transformers are still going to be made or what someone should do to fabricate either. I know I can't fabricate the transformer for sure and I guess with the layout I can get the PCB's made.

The rest of the Bill Of Materials (BOM) is in this thread right?? Sorry hard to read a 34 page thread and distill it down to the needed info although if I must I must

Thanks!!

Frannie

[Ed_Dinning]

Hi Frannie, yes, I wind the transformers to order and I can do a US pri 110/115 volts. I also fit a 2.5V heater tap for US types.
Problem is the high cost of poostage to the US.
I'm not sure if the PCBs are still available, but some menbers have built their Sussex using tag strip.

Ed

[squegging]

Hi,

This project looks really interesting, think I will give it a go. Got some 807's up in the loft that would be fun to test! Could someone shed some light on these queries before I start?

At the risk of querying the blindingly obvious, should the positive rail of the 48v supply be grounded? I can't see how it can work otherwise.

Has anyone come up with a solution to temperature stability of 100mV test signal?

Colin's comments about linearity of DPM readings are worrying. Perhaps if the Fluke and DPM were in parallel for this test, then I wonder if spillback noise was disturbing the readings and suggest that the comparison be repeated with only one meter connected at a time. Which supplier of DPM's is best?

Can anyone recommend a cheap case for this project?

Hope transformers are still available, am about to PM Ed Dinning

Keith

[Ed_Dinning]

Hi Folks, transformers are still available but are now wound on demand, so 2-3 weeks delivery.

Ed

[66barry]

I finally finished my tester and it works great but I need help with one problem I have. I used my own transformers to up the voltage to 400 volts and I modified the zener diode string to 400 volts. Now I am having problems blowing the TR1 ( MPSA92) and the 3 diodes(IN4148) when I switch to the TEST position on Function. I blew two transistors (TR1/MPSA92) before I finally installed a socket and cleaned up my traces on the board in case there was a short and now it works but I see arcing inside the 3 IN4148s when I switch it to test so I know I must be exceeding my parameters of the MPSA92. Can someone help me with the transistor maths and direct me to which parts to modify?

[Top Cap]

Originally Posted by squegging

Has anyone come up with a solution to temperature stability of 100mV test signal?

The 48V positive supply rail is grounded on the pcb, the link to 0V Ground was probably left off the original circuit for reasons of clarity.

There is a little drift on my Sussex build of the 100mV test signal but it does not worry me unduly. At switch on I measure 90mV which settles down after 30 minutes warm-up to a steady 100mV.

With regard to the panel meters - I have not done any tests on these myself, has this been confirmed as the usual performance of these meters or was it due to a faulty brand?

Les

[squegging]

Originally Posted by buglegirl

Sorry hard to read a 34 page thread and distill it down to the needed info although if I must I must

Frannie, you may find my extract of "relevant" posts helpful
Cheers
Keith

[kynsi73]

Hi all,

This looks like a great project so I'm going to build it. A few questions:

- In the anode and screen supply switch I see a lot of resistors in series and parallel. Can I substitute them for the combined values (1 x 75k instead of 2 x 150k parallel for instance), or is there a specific reason?
- can I use BC327 instead of BC307..

Thanks,
Corneel

[Top Cap]

In Mikes original circuit he did in fact use separate 75k resistors. Perhaps I am guilty of introducing the parallel resistors as I had loads of 150k but no 75k when I built my version. You should be able to use the BC327's too.

[Ed_Dinning]

Hi Corneel, You have a PM. If you do not have access to PM's yet due to low number of postings, then PM me again with your e-mail address and I will reply.


Ed

[ColinTheAmpMan1]

Hi All,
I have sourced some surplus thumbwheel switches from a seller in th USA. The switches were made by Chicago Dynamic Industries and cost $4.95 for a single three-section item. I bought six of these, as the seller said that two sections are 10-pole and the other is only 2-way. I Have taken some pictures and will try to post them, together with more info, as soon as I can. There are pictures on the sellers web-site , but there are no dimensions. Also, not all of these switches are the same - I will explain later.

The main difficulty is in the P+P and import charges. I thought that the seller's price was a giveaway, but the total with P+P came to $40.85 (£26.43). Not so bad, you might think, but when it eventually arrived in the UK I had to pay another £16.95 for import VAT and clearance. I suppose the total of £43.38 for six switches is still not so bad.

The URL of the switches on the website is:
http://www.electronicsurplus.com/Ite...0MTTD-200-630/

Regards, Colin.

[ColinTheAmpMan1]

Hi Guys,

The info on the thumbwheel switches is as follows:

Front escutcheon 60mm x 45mm.
Depth from front escutcheon to rear of switch 60mm.
Radius of switch wafer 10mm
Radius of contact tagstrip 15mm.

The front escutcheon is the front panel. The switch wafer is the actual rotary selector part of the switch, which is on the same piece of paxolin as the circular contact tagstrip.

As the seller notes, the first switch only shows 0 & 1, but the wafer itself has all 10 contacts and can be converted to a 10-way switch wafer by extracting a couple of metal limit-pins. This doesn't convert the switch completely, as the digits displayed are still only 0 & 1. I suppose some careful engraving and painting, or even a bit of printed sticky label would make a reasonable job of the missing display numbers.

The tracks on the wafers are about 1mm wide and are spaced apart by 1mm, which gives me some confidence as to the insulation properties.

While three of the switches that I purchased had three wafers each, another three had four. This extra wafer was twinned with the right-hand switch to make a two-pole 10-way switch. It could easily be eliminated (if necessary) by removing three screws and a supporting stand-off between the contact tagstrips. The extra length of the coupling between the rotary switch wafers is not a problem.

I am attaching some pictures of the switches, sometimes with a 10 pence piece (24mm in diameter) for scaling. Since I can only attach a maximum 5 images, the last two showing the extra pole will be attached to another message.

Regards, Colin.

[ColinTheAmpMan1]

And here are the pictures of the extra wafer, but without the 10p for scale.

I think these switches look good and are a lot cheaper than anything else I have seen. The seller still has quite a number left, but don't forget that you will need at least five, unless you are comfortable with converting the 0,1 switch and re-labelling the numbers on the thumbwheel.

Unfortunately, there don't seem to be any 9-position escutcheons for these switches that I have found. A three-by-three arrangement isn't too ugly, though.

Regards, Colin