Re: Homebrew Valve Tester
 

yes 6.3 volts is ok

Thanks

Re: Homebrew Valve Tester
 

I am not interested in a transformer but here are my thoughts on the subject:

Some of the power tubes have a plate dissipation in excess of 35 watts. It is always best to test a tube in a setting which is close to its intended use. Similarly some tubes are tested at 250V / 100mA anode current (e.g. 6L6-GC).

I found a toroid on eBay from a seller in Hong Kong which does 200 mA which is a bit overkill. When I was buying this I was aiming for a HT winding of 275 - 300 V @ 135 mA.

Hope this helps, AM.

Re: Homebrew Valve Tester
 

Hi !
I thought that the transformer was the tough part to get;
Before subscribing for the transformer, I had the idea to check availability of the DVM. It seems the seller has none of them to sell. (actually the Ebay shop is empty) So I wonder if the project is still feasible at low cost ???

Re: Homebrew Valve Tester
 

Hi All,
The last thing I thought there would be trouble with was the module.
I did a search on E Bay for "Blue LCD Meters" and a company called Asia Engineer has them in stock.
The tester will supply 250v @100mA OK, the current is limited to about 110mA. The transformer shows no sign of stress as it is only used for a short period of time.
Thanks to others who have given their heater requirements, will hold those on file.
Regards
Mike

Re: Homebrew Valve Tester
 

This is SO true, especially with the larger and more expensive valves.

25W should be OK for most valves. But the reason for running at high power is so that the internal metalwork and, to some extent, the glass envelope can get properly hot. This takes at least a couple of minutes.

A useful feature, if it's available, is the ability to run at high power for many hours. This can be an effective way of rescuing gassy valves. I've had about a 50% success rate with vintage KT66s. Since each one goes from being worth <£10 as a dead display item to >£50 as a working valve it can very quickly pay for a high current transformer. However I do realise that this is not what more than 90% of the unit's users will be doing with it. So if it would seriously increase the price then I'd say it probably isn't justified.

Cheers,

GJ

Re: Homebrew Valve Tester
 

Hi Gents, let's have a good discussion on this one.
I had thought of a seperate heater transformer for those who wanted a full compliment of taps.
It would also be possible at say, a 20% cost increment to have a higher current rating that was continous for soak tests. These could also be done at reduced anode voltage if the GB were also reduced (as we only need to get the valve hot, so a lower voltage tap would work).
Initial thoughts were to use an unshrouded transformer with mounting decided by the purchaser, but I know many of you take pride in the appearance of their equipment so I will see if shrouds for upright or drop through mounting are available. (not available for many lam sizes these days).

Keep the ideas coming.

Ed

Re: Homebrew Valve Tester
 

Hi everyone

Well done Mike on a great project.

Re the transformers, how about one of these for the HT
http://uk.rs-online.com/web/search/s...duct&R=5357783

and 1 or 2 of these for the 6v for the meter units
http://uk.rs-online.com/web/search/s...duct&R=3472464

Re the LT, for the people wanting a range, could this not be DC and variable using a LM317 or similar type device, say 0 - 40v with an additional 40v supply you can connect in series, monitored by another cheap meter unit?
http://uk.rs-online.com/web/search/s...duct&R=0805489

I don't know how the cost of these compares to a custom wound unit?

Richard

Re: Homebrew Valve Tester
 

This is going to need some hefty heatsinking to cover that voltage range at a high enough current to do some heaters. For example a 6080 with a 6.3V 2.5A heater would disspate over 80W in the regulator. I know this is an extreme example but it shows the potential problems. This is why multitap transformers are often seen as the best method. The alternative might be a switchmode regulator or pre-regulator.

Re: Homebrew Valve Tester
 

Or a variac on the primaries.......

Re: Homebrew Valve Tester
 

I know it may cause some re-design, but I have a qty of 70 of these devices if they would be of any use in the project. I certainly would not be asking the £25 I have seen them going for on web sites, more like £2.50.
Les

Re: Homebrew Valve Tester
 

An excellent project Mike, very professional.
I own an AVO VCM MK3 that is rather bulky compared to your design. When time permits, I'll have a go at building your circuit, it looks like a great project. I think that ferrite beads added to the valve base connections could be employed to minimise possible parasitic oscillations. This may be important as more bases are added.

Ed Dinning's suggestion of a separate transformer for the heater supply seems to be the best solution for a wide range of heater voltage requirements. Heavier duty switching may be required for the various heater ranges or separate wire jumpers could be employed.

Regards
Symon.

Re: Homebrew Valve Tester
 

I was hoping to use these switches, although the contact rating is given in the 100's of milliamps. it is also stated as being rated to 5 Amps.
Rather confusing but I was banking on the lower ratings as the breaking current and of course it is hoped that the switches would not be moved once set so can they be pushed to 5 Amps?
Les

Re: Homebrew Valve Tester
 

Les,

Care is needed with this type of switch. I have two here (no brand shown) which are superficially identical. However, one has MBB (make before break) contacts, the other is BBM (break before make). This initially caused me some confusion!

Edward

Re: Homebrew Valve Tester
 

Yes Edward, a local supplier here only does them as MBB and I nearly fell for those :D. I believe these are BBM, I have come across another Lorlin data sheet that seems to support my theory, i.e. will carry 5 Amps if uninterrupted.
Les

P.S. Yep, the 1024 is BBM with imperial shaft.

Re: Homebrew Valve Tester
 

Hi All,
further to the post regarding non availability of the LCD modules
http://shop.accessory4you.com/
list them as well as the address I originally gave

Mike

Re: Homebrew Valve Tester
 

Thank you Mike !
Again, Ebay in France is restricting some Ebay shops. I can go to the shop but it list it as empty.... Funny guys !
I'm seriously considering making one ;-)

Re: Homebrew Valve Tester
 

Hi Mike,
When do you think that a step by step guide will be available for the construction of your excellent project?

Thanks

Re: Homebrew Valve Tester
 

Hi Guitarist28 and others
The full details for the valve tester will appear in BVWS bulletin, although it must be said this is not a "blow by blow" account as much will depend on the casework and layout decided by each individual. Photographs of all salient points are included as are voltage measurements on the prototype.
There should be enough info on the forum to get things going, especially if Ed comes up with a transformer, which at the moment, general feedback suggests a single 6v heater winding will suffice. But there are still a few days for constructors to state their preferences.

Regards

Mike

Re: Homebrew Valve Tester
 

Hi Gents, yes there is always the question of switch carrying and breaking ratings as well as MBB and BBM.
On a tester I built many years ago, I used a simple plug board. H&S may be a problem if you need 117 volts but 50 should just be "in".
If we believe that a few heater voltages are required for everyday work these could be 4.0, 5.0, 6.3 and 12.6. The latter at under 1 A but the others need to be up to 3 A for some big rectifiers. There could be external sockets, or a switch for an external heater supply for the many other voltages that are encountered.

Ed

Re: Homebrew Valve Tester
 

I agree with that Ed, perhaps a fairly meaty secondary for those more hungry valves. To cater for the 1.4/2V directly heated valves, perhaps a rectifier and smoother fed by the 4V Tap and use a simple transistor regulator to switch it between 1.4 or 2V, the current would not be too much, especially the 1.4V types. I have very few battery valves but appreciate there are others who may have a special interest in these and would appreciate it. Obviously one cannot cater for all types, the range of heater voltages are too diverse so the option of a separate heater input is really a must. The transformer rating is complicated further by those wishing to have continuous running as an option in addition to just a quick test. Maybe the separate heater input terminals would also be a better option for continuous operation use.
Shrouds? If the transformer was visible perhaps, but for a piece of test gear an open transformer, with its cost reduction, would be quite acceptable here.
Les

Re: Homebrew Valve Tester
 

Hi Les tyhe adaptor is a good idea, it could also cater for the popular 2.5V US valves beloved of the audio fraternity.

Ed

Re: Homebrew Valve Tester
 

I personaly am going to concentrate on a few of valve base types that represent most of the useage in my collection of comms receivers. I like the idea of adapting for when there is the necessity to test more types, there are many easy ways of doing this. Nice and efficient on costs and complexity.

If you try to cater for all possibiliites there is a risk the transformer is going to price itself out of interest.

You know what it can be like sometimes the "what if's" can take over the design and turn it into something very expensive and complex for no real need.

Just my thought

Mike

Re: Homebrew Valve Tester
 

Does this tester have a name? "The Sword Valve Tester?"

Re: Homebrew Valve Tester
 

Hi Graham,
Never thought about a name, I just call it the VT1 (not a sexy name I know) as it's the first one I've built, but if you want a name for the forum or other reason, call it what you like (within reason!!!), as I'm Sussex born and bred possibly something to do with that. I'll leave it up to you

Regards
Mike
PS Amazed at the number of views

Re: Homebrew Valve Tester
 

'The Sussex VT' valve tester has a nice vintage ring to given the flavour of the forum.

I'm not suprised at the amount of replies that Swordholder has received given the resurgent interest in valves for all forms audio applications (including ipods)

Re: Homebrew Valve Tester
 

Mike.

As far as the forums go it doesn't matter whether your design has a name or not. I was just thinking that if large numbers of these get built builders/owners might want to refer to them by a name. Just as we might say "I've got an AVO CT160" or "I've got a Taylor 45C", builders could say "I've got a Sussex" and other people in the know would know what they were referring to.

If you're happy with the name "Sussex Valve Tester" I'll add it to the thread title, or you might prefer another name?

Re: The "Sussex" Homebrew Valve Tester.
 

Graham,
OK by me
Regards
Mike

Re: The "Sussex" Homebrew Valve Tester.
 

Hi Gents, I now have some lams for this transformer that I will try and get wound and sent off to Mike next week.
It looks as if it will fit on a 78 lam (95mm high, 80mm wide and a 40mm stack; about 70mm over the "belly").
It will have a 0-10-210-230-250 primary (110V can also be provided but as a different transformer).
0-250V at 120mA
0-30v at 20mA
0-6v at 50mA (times 3)
0-4-5-6.3 (@3A)-12.6v at 1A

I have yet to finalise the costing but this spec appears to be the minimum that is required. Inputs please.

For those who need a wider range of heater voltages I will look at an aux transformer, possibly about 2/3rds the size of the main one, which would have the heater voltages not supplied by the main unit. This would run from the 230V tap on the main transformer so that adjustment of the main input also sets the heater tranny.

Best regards, Ed

Re: The "Sussex" Homebrew Valve Tester.
 

Nice work ED

Mike

Re: The "Sussex" Homebrew Valve Tester.
 

Ed,
The spec looks good, there are a couple of mods I have in mind for the future so could the 30v winding be changed to 35v @ 50mA.
Are you going to have tags on the trnasformer for connections, and will it be a frame mounting type so it can be mounted in different orientations
Thanks for the good work
Regards
Mike

Re: The "Sussex" Homebrew Valve Tester.
 

Hi Mike, 35V at 50mA it is.
To keep the cost down I will make it a frame type with flying, colour coded leads. Leads will come out of one side only so it can be "drop through " mounted.
Angle brackets can then be used for upright mounting.
I'll post some pics when it is complete. Can you PM me your address please Mike.

Ed

Re: The "Sussex" Homebrew Valve Tester.
 

Sounds super Ed, for safety - will the transformer have an internal screen or are you using split bobbins?
Les

Re: The "Sussex" Homebrew Valve Tester.
 

Hi Les, it will be a screen, split bobbins give poor regulation

Ed

Re: The "Sussex" Homebrew Valve Tester.
 

Wow Ed I never knew that. Now I know why Lab Power Supplies always seem to use the normal (if I may call it that) type of single over wound bobbin.
Cheers
Les

Re: The "Sussex" Homebrew Valve Tester.
 

Hi Gents, here are some pics of the prototype transformer ready to go to Mike. It's not impregnated or over taped as it may need mods.
Size is 3 3/4" *3 1/8" and a 1 1/2" stack. It is 3" over the belly. FC's are 3 1/8" * 2 1/2"

Ed

Re: The "Sussex" Homebrew Valve Tester.
 

Hi Gents, costings etc now completed on this transformer.
It works out at £50 including UK postage (collect from Newcastle if you want a discount).

Could those who expressed interest please re-confirm by PM and any other interested parties also. I will then order the materials and the transformers will be available in about 3 to 4 weeks time.

Best regards, Ed

Re: The "Sussex" Homebrew Valve Tester.
 

Hi,

I'm new to both this forum and this thread.

This looks fascinating...

Will there be a PCB manufactured for a group buy?

Andy

Re: The "Sussex" Homebrew Valve Tester.
 

Yes!

In about 3 weeks.

It will be 1.6mm fibreglass,
I've ordered 50-off etched only from P&M services, undrilled, to keep the cost down.

Price yet to be determined to allow a royalty for Mike, (but likely to be nearer £10 inclusive than free or £20...) and, hopefully, cheaper than buying the necessary photo-resist board & chemicals for a 1-off.

Martin.

Re: The "Sussex" Homebrew Valve Tester.
 

In that case you can count me in for a PCB and transformer.

Nice one !!

Re: The "Sussex" Homebrew Valve Tester.
 

Hi Gents, when you PM me for transformers please include your postal address. I'll let you know when they are being sent off and you can then pay me by cash or cheque,

Best regards, Ed

Re: The "Sussex" Homebrew Valve Tester.
 

Swordholder, could I get away with just two front panel meters?
I happen to have two Lascar single hole mounting panel meters, could I switch one to measure Anode/Screen current and the other Grid V/Gm or would this be inconvenient in practice?
Les

Re: The "Sussex" Homebrew Valve Tester.
 

Hi Top Cap,
There is no reason why you have to have 3 meters. You can switch, but bear in mind that the GM meter measures AC millivolts to a resolution of 0.1mV.
Obviously the meter sensitivity will have to taken into consideration, again the anode current meter is a 199.9mv DC meter with a resolution of 0.1mV.
I don't know the Lascar meters, are they analogue or digital.
I used the 3 meters because (a) they dont need any switching and (b) they are relatively cheap at around £6 each including carriage on E Bay (see my previous posts for address).
If you do use the Lascar meters, you may have to alter values of resistors around the circuit.

Regards

Mike

Re: The "Sussex" Homebrew Valve Tester.
 

Mike,

Is there any chance that you could produce a BOM for this.

Regards

Andy

Re: The "Sussex" Homebrew Valve Tester.
 

Andy,
I don't have a BOM, but the component values are all on the ciruit I published, any additions has been covered in my subsequent postings.
If you have any query let me know and I will try to answer your query
.

Regards
Mike

Re: The "Sussex" Homebrew Valve Tester.
 

Mike,

Yes, I've gleamed what I can from the published threads.

I guess it's just things such as resistor ratings (1/8w, 1/4w etc) and capacitor voltage ratings, part numbers of the switches you used, etc. etc.

If I can get all the info I'd be happy to put a BOM together that anyone can refer to.

Re: The "Sussex" Homebrew Valve Tester.
 

OK,

I have put together a basic BOM for this.
Things I am missing......

Valve bases
Most Switches
Resistor ratings
Capacitor voltage ratings

Feel free to tell me what I've done wrong and suggest ratings, switches etc.

Andy

Link to BOM

http://spreadsheets.google.com/ccc?k...pfMlE&hl=en_GB

Re: The "Sussex" Homebrew Valve Tester.
 

That supplier presently shows no stock on e-bay, as does a firm I've used called Virtual Village. Maybe that's a temporary state of affairs. I hope so - these are great little meters, and as cheap if not cheaper than analogue meters, and being backlit, are nice and clear.

David,
G4EBT

Re: The "Sussex" Homebrew Valve Tester.
 

Dave,

Asia Engineer on Ebay have them in stock, I ordered a set today.

http://cgi.ebay.com/ws/eBayISAPI.dll...m=370325100729


Regards
Mike

Re: The "Sussex" Homebrew Valve Tester.
 

Andy,
Excellent!
A starter:
Add 2 1N4007s if using Ed's transformer, to make a bridge with D1 & D2,
D8-11 could be any 1N400x,
R2 dissipates about 0.75W, so perhaps a 2-watter, stood off the PCB?
Martin.

Re: The "Sussex" Homebrew Valve Tester.
 

Andy,
The majority of the resistors (apart from the one Martin mentioned) are 0.6w MF fron Rapid electronics
Switches are
2 x 1p 12w Make before Break rotary switches (Rapid Electronics 79-0100) Anode/G2 volts
1 x 3p 4w rotary switch (Rapid Electronics 79-0222) Function switch
10 x 1p 12w rotary switch (Rapid Electronics 79-0220)
(A1/A2 sel + pin selectors)
Relays are
Relays 2 x 48v low profile 8A (Rapid Electronics 60-4854 or similar
LEDS
LED1 Standard green LED
LED on relay board Standard Green LED
LED2 LED3 Low Current red LED (Rapid Electronics 56-0430 or similar
Hope this helps.

Regards
Mike