OTH2 as EM35 replacement? - UK Vintage Radio Repair and Restoration Discussion Forum

longneck90 · 22nd Apr 2017, 4:59 pm

Hello to everyone. I was hoping that some of the Forum members might have information about the following. Recently, I sent to a Russian valve company for a replacement for EM35. Consequently, a OTH2 arrived. I installed OTH2 and switched on radio.
When the radio warmed up, I felt something was not quite right. After about 40 seconds, the tuned station disappeared, and at the same time I thought I felt as if something was heating up, and switched radio off. I removed OTH2, switched radio on again, and it is working OK. The OTH2 did not exhibit any green signal light when expected to. I am unable to find out any information about OTH2, to compare it with EM35. I was wondering, therefore, if any Forum members know anything about OTH2, or whether it is a proper replacement for EM35. Thanks in advance, all the best. John.

Sideband · 22nd Apr 2017, 5:05 pm

I've not heard of either valve. Are you sure EM35 is right? What model set are you working on?

ukcol · 22nd Apr 2017, 5:22 pm

Some info on the EM35 here.

I don't know the OTH2 though.

Leon Crampin · 22nd Apr 2017, 5:46 pm

The grid and target pins are transposed between some of the octal based tuning indicators. It's essential to check before making substitutions.

Leon.

turretslug · 22nd Apr 2017, 6:01 pm

Are there any other markings on the valve? Some Russian valves have a prominent "OTK(number)" approval mark on the base and a somewhat faint type identification on the bulb.

(Perhaps "Office of the Technical Commissariat"?)

Sideband · 22nd Apr 2017, 6:48 pm

Judging by the comments on the Radiomuseum site it would seem that other substitutes are not pin compatible. You'll need info on both valves before swapping them. A base rewire is most likely necessary.

longneck90 · 23rd Apr 2017, 1:30 pm

Hello, and thanks to all who responded to my query about EM 35 'substitute'. EM 35 is in the Nordmende Tannhauser radio. The identity markings on OTH2 are almost gone now, and so I am unable to photograph them. There are no other markings. If I knew the Pin data, and voltages of OTH2, I could rewire base. But... so far, I can't find anything about OTH2. Anyway, thanks again. All the best. John.

Alistair D · 23rd Apr 2017, 2:11 pm

The only thing I found was this..

http://www.tubebooks.org/Russian.htm

Looks like it be a bit of a laborious task though.

Al

ms660 · 23rd Apr 2017, 2:41 pm

One of the most common Russian magic eye valves is the 6E5c, I'm wondering if the OP's valve is one of them, some details about the different pin connections here (scroll down):

http://www.radiomuseum.org/tubes/tube_em34.html

Lawrence.

cmjones01 · 23rd Apr 2017, 7:16 pm

The 'OTH' marking is most likely 'OTK': the 'K' on photos of Russian valves I've seen does look very much like an H. I think this is the approval marking, not the valve type. A 6E5C is the most likely candidate.

Chris

longneck90 · 23rd Apr 2017, 8:40 pm

Hello to everyone, and thanks for all the information about EM35/OTH2. I looked at Radiomuseum, under EM35, and I do see information including pinout, about valve 6E5C, which I am now convinced, is the new valve I have. (the valve that is marked OTH2). I can see that the pinout is different from EM35, and so, will change wiring. I don't know why I ordered this valve (OTH2 ?) in the first place, as I could have got the proper valve here in GB cheaper. Thanks again to everyone. All the best. John.

22nd Apr 2017, 4:59 pm	#1
longneck90 Hexode Join Date: Sep 2013 Location: Wembley, London, UK. Posts: 395	OTH2 as EM35 replacement? Hello to everyone. I was hoping that some of the Forum members might have information about the following. Recently, I sent to a Russian valve company for a replacement for EM35. Consequently, a OTH2 arrived. I installed OTH2 and switched on radio. When the radio warmed up, I felt something was not quite right. After about 40 seconds, the tuned station disappeared, and at the same time I thought I felt as if something was heating up, and switched radio off. I removed OTH2, switched radio on again, and it is working OK. The OTH2 did not exhibit any green signal light when expected to. I am unable to find out any information about OTH2, to compare it with EM35. I was wondering, therefore, if any Forum members know anything about OTH2, or whether it is a proper replacement for EM35. Thanks in advance, all the best. John.

22nd Apr 2017, 5:05 pm	#2
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,580	Re: EM35 replacement I've not heard of either valve. Are you sure EM35 is right? What model set are you working on? __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

22nd Apr 2017, 5:22 pm	#3
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: EM35 replacement Some info on the EM35 here. I don't know the OTH2 though.

22nd Apr 2017, 5:46 pm	#4
Leon Crampin Octode Join Date: Nov 2005 Location: Surrey, UK. Posts: 1,874	Re: OTH2 as EM35 replacement? The grid and target pins are transposed between some of the octal based tuning indicators. It's essential to check before making substitutions. Leon.

22nd Apr 2017, 6:01 pm	#5
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,400	Re: OTH2 as EM35 replacement? Are there any other markings on the valve? Some Russian valves have a prominent "OTK(number)" approval mark on the base and a somewhat faint type identification on the bulb. (Perhaps "Office of the Technical Commissariat"?) Last edited by turretslug; 22nd Apr 2017 at 6:28 pm.

22nd Apr 2017, 6:48 pm	#6
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,580	Re: OTH2 as EM35 replacement? Judging by the comments on the Radiomuseum site it would seem that other substitutes are not pin compatible. You'll need info on both valves before swapping them. A base rewire is most likely necessary. __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

23rd Apr 2017, 1:30 pm	#7
longneck90 Hexode Join Date: Sep 2013 Location: Wembley, London, UK. Posts: 395	Re: OTH2 as EM35 replacement? Hello, and thanks to all who responded to my query about EM 35 'substitute'. EM 35 is in the Nordmende Tannhauser radio. The identity markings on OTH2 are almost gone now, and so I am unable to photograph them. There are no other markings. If I knew the Pin data, and voltages of OTH2, I could rewire base. But... so far, I can't find anything about OTH2. Anyway, thanks again. All the best. John.

23rd Apr 2017, 2:11 pm	#8
Alistair D Nonode Join Date: Jan 2010 Location: Edinburgh, UK. Posts: 2,008	Re: OTH2 as EM35 replacement? The only thing I found was this.. http://www.tubebooks.org/Russian.htm Looks like it be a bit of a laborious task though. Al __________________ I won't tell you how I discovered that.

23rd Apr 2017, 2:41 pm	#9
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: OTH2 as EM35 replacement? One of the most common Russian magic eye valves is the 6E5c, I'm wondering if the OP's valve is one of them, some details about the different pin connections here (scroll down): http://www.radiomuseum.org/tubes/tube_em34.html Lawrence.

23rd Apr 2017, 7:16 pm	#10
cmjones01 Nonode Join Date: Oct 2008 Location: Warsaw, Poland and Cambridge, UK Posts: 2,681	Re: OTH2 as EM35 replacement? The 'OTH' marking is most likely 'OTK': the 'K' on photos of Russian valves I've seen does look very much like an H. I think this is the approval marking, not the valve type. A 6E5C is the most likely candidate. Chris __________________ What's going on in the workshop? http://martin-jones.com/

23rd Apr 2017, 8:40 pm	#11
longneck90 Hexode Join Date: Sep 2013 Location: Wembley, London, UK. Posts: 395	Re: OTH2 as EM35 replacement? Hello to everyone, and thanks for all the information about EM35/OTH2. I looked at Radiomuseum, under EM35, and I do see information including pinout, about valve 6E5C, which I am now convinced, is the new valve I have. (the valve that is marked OTH2). I can see that the pinout is different from EM35, and so, will change wiring. I don't know why I ordered this valve (OTH2 ?) in the first place, as I could have got the proper valve here in GB cheaper. Thanks again to everyone. All the best. John.