Resco GDM-8 Grid Dip Oscillator - UK Vintage Radio Repair and Restoration Discussion Forum

Scrapheap · 11th Mar 2017, 6:52 pm

I recently obtained one of these on eBay. It's Japanese made with 6AM4 valve I think, very solid construction and complete with set of plug-in coils. Cannot find any info or handbook on the web at all, anybody ever had one??

Bazz4CQJ · 11th Mar 2017, 9:56 pm

Resco is not a brand that I have heard of previously, but sometimes products were sold in different countries under different names. I keep notes on just about every GDO I ever encounter.

What we need....is a picture

.

B

Scrapheap · 12th Mar 2017, 12:01 pm

Hi Bazz,

Thanks a lot for the quick reply - you're just what I need, a GDO-collector!
Here's the picture, second time lucky, my last reply vanished before <I could complete it! Actually, this unit is very sturdily made with a heavy metal case. I think it works but the deflection I got on testing a MW Rx was very faint, compared to my other GDO which is a Grundig transistor TR 300.

Many thanks for your help - what would be very useful at this point is a manual.
Best wishes,

Chris (HB9HFB)

Radio Wrangler · 12th Mar 2017, 12:06 pm

A neat looking instrument. If no information turns up, at least the circuit should not be difficult to trace out.

Usually valve-based dip meters give clearer indications than transistor ones do, so you may have a fault in this one.

David

IanG3XYV · 12th Mar 2017, 4:13 pm

I have one of these but it's labelled Kyoritsu. I bought it new around 1968. Had some problems with the mains transformer but managed to rework it and it functions as it did. I don't recall the dip being very pronounced though.

I found the circuit on the net and have attached it here.

Ian

IanG3XYV · 12th Mar 2017, 4:14 pm

Forgot to say the valve is a 6AF4A.

Scrapheap · 12th Mar 2017, 5:48 pm

Dear Ian and Bazz,

Thanks a lot for the feedback and Ian, for the schematic. Looks like it might be worth replacing a couple of caps and checking the valve on my trusty Hickok 600, which is made for testing American tubes!

David G4EBT · 12th Mar 2017, 7:01 pm

Interesting to see that is uses three 1pF 'gimmick' capacitors - just a couple of turns of insulated wire taken to ground. Value not critical.

I guess that the use of the archaic term 'uuF' rather than 'pF' dates it to maybe the 1950s or even a bit earlier?

Looks a nice piece of kit and luckily, with it's coils intact too.

ms660 · 12th Mar 2017, 7:07 pm

Maybe 1,000pF feedthroughs?

Lawrence.

David G4EBT · 12th Mar 2017, 7:36 pm

Ah Yes - I read1.000 uuf as 1pF but I guess it was 1,000 uuF, so you may well be right Lawrence.

Bazz4CQJ · 12th Mar 2017, 10:09 pm

And if we look at the very recent Post#33 in this thread http://www.vintage-radio.net/forum/s...=134225&page=2 we find the same GDO was sold under the brand "Honor"; apparently very popular in Australasia.

The circuits of valve GDO's rarely deviate from a pretty standard design, so if some work better than others you'd have to think it was in the way they were was constructed.

I must get round to building a valve GDO.... or should I do the tunnel diode one first, as per Heathkit (it works on just 1.5V and yes, I have a suitable tunnel diode...I think) ?

B

Alistair D · 13th Mar 2017, 12:52 am

I suspect Kyoritsu will have been the original manufacturer. Many of their products appeared under different names including Eagle International.

Bazz: If you are considering a valve based GDO this looks like an interesting alternative approach. Post #17 on this thread.
https://www.vintage-radio.net/forum/...d.php?t=107489

Al

Bazz4CQJ · 13th Mar 2017, 1:52 am

Well, the bad thing about that thread is that I was clearly talking about building a valve GDO back in 2014..and it's still all talk

.

The EM valve is interesting, but I'd like to make a valve GDO which could be run on batteries so it is portable, and there's an Acorn valve with a 1.5V filament which fits that bill perfectly

. The American "Megacycle Meter", built in the late 1940's and claimed by some to be an exceptionally good GDO, also used an Acorn valve.

I loved stuff made by Eagle!

B

11th Mar 2017, 9:56 pm	#2
Bazz4CQJ Dekatron Join Date: Apr 2009 Location: Oxfordshire, UK. Posts: 4,935	Re: Resco GDM-8 Grid Dip Oscillator Resco is not a brand that I have heard of previously, but sometimes products were sold in different countries under different names. I keep notes on just about every GDO I ever encounter. What we need....is a picture . B __________________ Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch.

12th Mar 2017, 12:06 pm	#4
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,903	Re: Resco GDM-8 Grid Dip Oscillator A neat looking instrument. If no information turns up, at least the circuit should not be difficult to trace out. Usually valve-based dip meters give clearer indications than transistor ones do, so you may have a fault in this one. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

12th Mar 2017, 4:14 pm	#6
IanG3XYV Pentode Join Date: Sep 2014 Location: Bedford, Bedfordshire, UK. Posts: 174	Re: Resco GDM-8 Grid Dip Oscillator Forgot to say the valve is a 6AF4A.

12th Mar 2017, 5:48 pm	#7
Scrapheap Triode Join Date: Jul 2013 Location: Basel, Switzerland Posts: 25	Re: Resco GDM-8 Grid Dip Oscillator Dear Ian and Bazz, Thanks a lot for the feedback and Ian, for the schematic. Looks like it might be worth replacing a couple of caps and checking the valve on my trusty Hickok 600, which is made for testing American tubes!

12th Mar 2017, 7:01 pm	#8
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,767	Re: Resco GDM-8 Grid Dip Oscillator Interesting to see that is uses three 1pF 'gimmick' capacitors - just a couple of turns of insulated wire taken to ground. Value not critical. I guess that the use of the archaic term 'uuF' rather than 'pF' dates it to maybe the 1950s or even a bit earlier? Looks a nice piece of kit and luckily, with it's coils intact too. __________________ David. BVWS Member. G-QRP Club member 1339.

11th Mar 2017, 6:52 pm	#1
Scrapheap Triode Join Date: Jul 2013 Location: Basel, Switzerland Posts: 25	Resco GDM-8 Grid Dip Oscillator I recently obtained one of these on eBay. It's Japanese made with 6AM4 valve I think, very solid construction and complete with set of plug-in coils. Cannot find any info or handbook on the web at all, anybody ever had one??

12th Mar 2017, 12:01 pm	#3
Scrapheap Triode Join Date: Jul 2013 Location: Basel, Switzerland Posts: 25	Re: Resco GDM-8 Grid Dip Oscillator Hi Bazz, Thanks a lot for the quick reply - you're just what I need, a GDO-collector! Here's the picture, second time lucky, my last reply vanished before <I could complete it! Actually, this unit is very sturdily made with a heavy metal case. I think it works but the deflection I got on testing a MW Rx was very faint, compared to my other GDO which is a Grundig transistor TR 300. Many thanks for your help - what would be very useful at this point is a manual. Best wishes, Chris (HB9HFB) Attached Thumbnails

12th Mar 2017, 7:07 pm	#9
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Resco GDM-8 Grid Dip Oscillator Maybe 1,000pF feedthroughs? Lawrence.

12th Mar 2017, 7:36 pm	#10
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,767	Re: Resco GDM-8 Grid Dip Oscillator Ah Yes - I read1.000 uuf as 1pF but I guess it was 1,000 uuF, so you may well be right Lawrence. __________________ David. BVWS Member. G-QRP Club member 1339.

12th Mar 2017, 10:09 pm	#11
Bazz4CQJ Dekatron Join Date: Apr 2009 Location: Oxfordshire, UK. Posts: 4,935	Re: Resco GDM-8 Grid Dip Oscillator And if we look at the very recent Post#33 in this thread http://www.vintage-radio.net/forum/s...=134225&page=2 we find the same GDO was sold under the brand "Honor"; apparently very popular in Australasia. The circuits of valve GDO's rarely deviate from a pretty standard design, so if some work better than others you'd have to think it was in the way they were was constructed. I must get round to building a valve GDO.... or should I do the tunnel diode one first, as per Heathkit (it works on just 1.5V and yes, I have a suitable tunnel diode...I think) ? B __________________ Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch.

13th Mar 2017, 12:52 am	#12
Alistair D Nonode Join Date: Jan 2010 Location: Edinburgh, UK. Posts: 2,008	Re: Resco GDM-8 Grid Dip Oscillator I suspect Kyoritsu will have been the original manufacturer. Many of their products appeared under different names including Eagle International. Bazz: If you are considering a valve based GDO this looks like an interesting alternative approach. Post #17 on this thread. https://www.vintage-radio.net/forum/...d.php?t=107489 Al __________________ I won't tell you how I discovered that.

13th Mar 2017, 1:52 am	#13
Bazz4CQJ Dekatron Join Date: Apr 2009 Location: Oxfordshire, UK. Posts: 4,935	Re: Resco GDM-8 Grid Dip Oscillator Well, the bad thing about that thread is that I was clearly talking about building a valve GDO back in 2014..and it's still all talk . The EM valve is interesting, but I'd like to make a valve GDO which could be run on batteries so it is portable, and there's an Acorn valve with a 1.5V filament which fits that bill perfectly . The American "Megacycle Meter", built in the late 1940's and claimed by some to be an exceptionally good GDO, also used an Acorn valve. I loved stuff made by Eagle! B __________________ Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch.