Grundig 3365 mains transformer - UK Vintage Radio Repair and Restoration Discussion Forum

andrewn · 20th Nov 2019, 9:22 pm

A few weeks ago I posted about a Grundig 3365 I saw in a local shop. A week or so later it was still there so I bought it.
I've put it on the workbench and initial testing with a multimeter finds that the 220v primary (w/82R resistor in series) is o/c. The 110V tapping still has continuity. The obvious solution is to operate the radio on 110V via a step-down transformer. I will disconnect the loads and see if it outputs the correct voltages with a 110V supply.

On the circuit diagram it shows the ECC83 heater being supplied from a separate winding than the other valves. Can anyone advise why this is done? The circuit diagram for the similar 3395 model has all valves on the same winding. If I need to fit a modern transformer it's easier to buy one with a single 6.3 winding.
Thanks, Andrew.

G0HFCFrank · 20th Nov 2019, 9:51 pm

Hi Andrew,
The ECC83 is the audio amplifier/phase splitter driving the push-pull output stage. You will notice the separate heater supply to this valve has a centre tap to ground and I would guess this is to reduce mains hum.
Frank C.

Chris55000 · 21st Nov 2019, 11:55 am

Hi!

Ed Dinning would be able to rewind this with 115, 225 & 245V primary taps for you if needed, or, if you're not too bothered about an "original":look, you can get valve type "R Core Transformers" with more than one 6.3V winding to suit your Grundig circuit!

Chris Williams

turretslug · 21st Nov 2019, 12:03 pm

I expect that you've been down this route already, but it might be worth closely checking the end of the 220V winding where it emerges from the bobbin and connects to the terminal- if you're really lucky, it might just have parted here and be recoverable with a bit of careful surgery. Just a thought!

andrewn · 21st Nov 2019, 10:19 pm

Thanks for your help. I peeled back some of the insulation but there doesn't seem to be a break in the wire. I'm not sure if the transformer has been burnt out. The 82R resistor had burnt the mains lead and an incorrect fuse was fitted. A 25uF capacitor had burst open as well. Other than that the radio is in good condition.
I disconnected the secondaries and powered up the transformer on 115V from my shaver socket. I measured HT winding 271V, yellow winding 7.4V and blue winding 7.6V. I'm not clear with the circuit diagram as it says "278V 69ma/270V 73ma. I assume this is the rectified DC voltage and therefore the AC voltage should be somewhat less?

If I buy a new transformer would this be suitable? https://primarywindings.com/product/pwht02/

'LIVEWIRE?' · 21st Nov 2019, 10:50 pm

Those readings sound OK to me, Andrew. 271v AC with no load should be about right, and the two LT windings' voltages should drop to approx 6.3v on load. From that and from the figures quoted for the transformer in your link, provided it will physically fit, unless I'm missing something, it should be OK as a replacement. Incidentally, the two different HT voltages are what would be expected from changes in the current drawn

turretslug · 22nd Nov 2019, 7:59 pm

I think those two slightly different HT voltage/current ratings are likely to be the difference between AM and FM modes, i.e. switching the triode of the ECHxx off, and the double-triode of the ECC85 (or similar) on. Or something along those lines. That transformer linked to certainly sounds as though it has plenty of HT capability- it looks as though it can be used in either 2-diode full-wave bi-phase rectifier mode (centre-tapped with series secondaries), or 4-diode bridge rectifier mode with paralleled secondaries. 160mA of AC current capability approximates to about 100mA bridge-rectified DC output.

I'd not heard of Primary Windings before, but it looks as if they offer some useful transformer options there.

Ed_Dinning · 22nd Nov 2019, 8:39 pm

Hi Andrew those readings sound OK, you could test it by allowing it to run for say 1/2 hour under those conditions and with no valves fitted. The transformer should then only be slightly warm to the touch.

Ed

andrewn · 9th May 2020, 2:39 pm

I just thought I would update this thread. I bought the above mentioned transformer and is all working well. Before I bought the transformer I bought a very cheap 12v to 110v inverter. This enabled me to power up the radio with its original transformer to see what else was faulty. All that needed replacing was a small electrolytic cap and the 1K resistor on top the o/p transformer. After I had replaced those the radio worked. I then replaced the wax caps for reliability. I didn't need to replace the reservoir cap as it tests fine.
On fitting the new transformer I decided to replace the selenium rectifier at the same time. I also made use of the fuse board to add a fuse for the HT. I fitted a plastic sheet between the fuse board and transformer for extra safety. The radio is meant to be double-insulated and has the symbol on the back panel.
I also re-painted behind the tuning scale and fixed the slipping tuning clutch when on VHF.

vinrads · 8th Jun 2020, 11:45 pm

Good job , Nice radio well done ,Mick.

20th Nov 2019, 9:22 pm	#1
andrewn Pentode Join Date: Aug 2008 Location: Taunton, Somerset, UK. Posts: 135	Grundig 3365 mains transformer A few weeks ago I posted about a Grundig 3365 I saw in a local shop. A week or so later it was still there so I bought it. I've put it on the workbench and initial testing with a multimeter finds that the 220v primary (w/82R resistor in series) is o/c. The 110V tapping still has continuity. The obvious solution is to operate the radio on 110V via a step-down transformer. I will disconnect the loads and see if it outputs the correct voltages with a 110V supply. On the circuit diagram it shows the ECC83 heater being supplied from a separate winding than the other valves. Can anyone advise why this is done? The circuit diagram for the similar 3395 model has all valves on the same winding. If I need to fit a modern transformer it's easier to buy one with a single 6.3 winding. Thanks, Andrew.

20th Nov 2019, 9:51 pm	#2
G0HFCFrank Pentode Join Date: Oct 2011 Location: Oldham, Greater Manchester, UK. Posts: 167	Re: Grundig 3365 mains transformer Hi Andrew, The ECC83 is the audio amplifier/phase splitter driving the push-pull output stage. You will notice the separate heater supply to this valve has a centre tap to ground and I would guess this is to reduce mains hum. Frank C.

21st Nov 2019, 11:55 am	#3
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,869	Re: Grundig 3365 mains transformer Hi! Ed Dinning would be able to rewind this with 115, 225 & 245V primary taps for you if needed, or, if you're not too bothered about an "original":look, you can get valve type "R Core Transformers" with more than one 6.3V winding to suit your Grundig circuit! Chris Williams

21st Nov 2019, 12:03 pm	#4
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,395	Re: Grundig 3365 mains transformer I expect that you've been down this route already, but it might be worth closely checking the end of the 220V winding where it emerges from the bobbin and connects to the terminal- if you're really lucky, it might just have parted here and be recoverable with a bit of careful surgery. Just a thought!

21st Nov 2019, 10:19 pm	#5
andrewn Pentode Join Date: Aug 2008 Location: Taunton, Somerset, UK. Posts: 135	Re: Grundig 3365 mains transformer Thanks for your help. I peeled back some of the insulation but there doesn't seem to be a break in the wire. I'm not sure if the transformer has been burnt out. The 82R resistor had burnt the mains lead and an incorrect fuse was fitted. A 25uF capacitor had burst open as well. Other than that the radio is in good condition. I disconnected the secondaries and powered up the transformer on 115V from my shaver socket. I measured HT winding 271V, yellow winding 7.4V and blue winding 7.6V. I'm not clear with the circuit diagram as it says "278V 69ma/270V 73ma. I assume this is the rectified DC voltage and therefore the AC voltage should be somewhat less? If I buy a new transformer would this be suitable? https://primarywindings.com/product/pwht02/ Attached Thumbnails

21st Nov 2019, 10:50 pm	#6
'LIVEWIRE?' Rest in Peace Join Date: Mar 2006 Location: N.W. Oxfordshire(Chipping Norton) Posts: 7,306	Re: Grundig 3365 mains transformer Those readings sound OK to me, Andrew. 271v AC with no load should be about right, and the two LT windings' voltages should drop to approx 6.3v on load. From that and from the figures quoted for the transformer in your link, provided it will physically fit, unless I'm missing something, it should be OK as a replacement. Incidentally, the two different HT voltages are what would be expected from changes in the current drawn

22nd Nov 2019, 7:59 pm	#7
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,395	Re: Grundig 3365 mains transformer I think those two slightly different HT voltage/current ratings are likely to be the difference between AM and FM modes, i.e. switching the triode of the ECHxx off, and the double-triode of the ECC85 (or similar) on. Or something along those lines. That transformer linked to certainly sounds as though it has plenty of HT capability- it looks as though it can be used in either 2-diode full-wave bi-phase rectifier mode (centre-tapped with series secondaries), or 4-diode bridge rectifier mode with paralleled secondaries. 160mA of AC current capability approximates to about 100mA bridge-rectified DC output. I'd not heard of Primary Windings before, but it looks as if they offer some useful transformer options there.

22nd Nov 2019, 8:39 pm	#8
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 8,194	Re: Grundig 3365 mains transformer Hi Andrew those readings sound OK, you could test it by allowing it to run for say 1/2 hour under those conditions and with no valves fitted. The transformer should then only be slightly warm to the touch. Ed

9th May 2020, 2:39 pm	#9
andrewn Pentode Join Date: Aug 2008 Location: Taunton, Somerset, UK. Posts: 135	Re: Grundig 3365 mains transformer I just thought I would update this thread. I bought the above mentioned transformer and is all working well. Before I bought the transformer I bought a very cheap 12v to 110v inverter. This enabled me to power up the radio with its original transformer to see what else was faulty. All that needed replacing was a small electrolytic cap and the 1K resistor on top the o/p transformer. After I had replaced those the radio worked. I then replaced the wax caps for reliability. I didn't need to replace the reservoir cap as it tests fine. On fitting the new transformer I decided to replace the selenium rectifier at the same time. I also made use of the fuse board to add a fuse for the HT. I fitted a plastic sheet between the fuse board and transformer for extra safety. The radio is meant to be double-insulated and has the symbol on the back panel. I also re-painted behind the tuning scale and fixed the slipping tuning clutch when on VHF. Attached Thumbnails

8th Jun 2020, 11:45 pm	#10
vinrads Dekatron Join Date: Feb 2009 Location: Chesterfield, Derbyshire, UK. Posts: 3,762	Re: Grundig 3365 mains transformer Good job , Nice radio well done ,Mick.