8mm Forum: Exciter lamp power

This is topic Exciter lamp power in forum 16mm Forum at 8mm Forum.

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Posted by Terry Sills (Member # 3309) on June 24, 2015, 01:53 AM:

I have an RCA Hollywood that suffers low sound. The amplifier is fine but film sound is low. I have checked and cleaned all the optics but the exciter lamp seems a little dim. It is powered it seems from the amplifier and I'm wondering how I can increase the voltage a little. Is there a particular valve that drives the exciter lamp? Or is there something else that might need replacing.

Posted by Maurice Leakey (Member # 916) on June 24, 2015, 02:29 AM:

The exciter lamp is fed from the oscillator valve V7, this is a 6V6-GT. There is no method of changing the voltage.

Posted by Terry Sills (Member # 3309) on June 24, 2015, 02:52 AM:

Thanks Maurice
So if this valve is weak could replacing it make a difference? Other than that the transformer trappings are for a range 215 - 250v and as we are on 230v, could it be that this is the reason.

Posted by Maurice Leakey (Member # 916) on June 24, 2015, 03:19 AM:

Certainly. Either replace the valve, or the exciter lamp.
I don't think altering the mains input voltage is a good idea.

Posted by Paul Mason (Member # 4015) on June 24, 2015, 03:57 AM:

Terry,
Have you tried shining a pencil torch on the photocell? If the exciter lamp output is the problem you should be able to generate loud thumps in the speaker. Be careful of the speaker though and turn up the volume cautiously.

Posted by Terry Sills (Member # 3309) on June 24, 2015, 07:10 AM:

Paul
Yes the PEC is working fine. What I have also tried is connecting the exciter lamp to an external power source and putting 4 volts through it . The lamp was brighter and it gave more volume but it caused a bit of hum as well even though it was DC voltage.

Posted by Paul Mason (Member # 4015) on June 24, 2015, 08:10 AM:

Terry,
What was also in mind apart from the PEC is the amplifier gain. The amplifier should be able to create a loud noise in the speaker. If not then the amp is suspect.

Posted by Terry Sills (Member # 3309) on June 24, 2015, 10:51 AM:

Paul
What makes me think the amp is good is that when I plug a Mike in there is loads of volume, but is this on the same circuit as the PEC? And is it a good indication that the amp is good.

Posted by Maurice Leakey (Member # 916) on June 24, 2015, 02:50 PM:

The P.E.C. and the mic socket J-1 both connect to the grid of V-1. a 6J7.
The exciter lamp is, indeed, rated at 0.75 amp, 4 volts.

Posted by Terry Sills (Member # 3309) on June 24, 2015, 03:02 PM:

Maurice
The Hollywood doesn't have 6V6 GT valves. They have EL84's, EF86's, ECC83 and EZ81. Do you know which one would control the exciter lamp?

Posted by Martin Jones (Member # 1163) on June 24, 2015, 03:29 PM:

The only one of those capable of generating sufficient power to drive an exciter lamp is the EL84. How many EL84s does it have?
Martin

Posted by Maurice Leakey (Member # 916) on June 25, 2015, 03:00 AM:

Agree with Martin.
The 6V6GT is an output valve. The EL84 is a later type output valve with small pins B9A base. It is smaller and more sensitive than the 6VG.
I believe they are still manufactured, probably in Russia.

Posted by Terry Sills (Member # 3309) on June 25, 2015, 03:30 AM:

Martin
There is a EL84 coupled with a EZ81 and then in the main part of the amp there are two EL84's an ECC83 and two EF86's. At the top of the amp close to the EL84 and the EZ81 there is a plug with a wire leading to the exciter lamp and at the bottom of the amp near an EF86 is a plug and wire which looks like it might be feeding the PEC. Does this make any sense to you?

Posted by Maurice Leakey (Member # 916) on June 25, 2015, 03:54 AM:

I mentioned above that the Mic/P.E.C. feed to V1 which in my diagram was shown as a 6J7. This valve was used for an audio amplifier input stage.
The EF86 is a later equivalent introduced by Mullard in 1954, so you are correct.

Posted by Terry Sills (Member # 3309) on June 25, 2015, 04:01 AM:

Maurice
I've tried replacing the EL84 next to the Ez81 - no difference. I'm now going to try replacing the EF86 that you say drives the PEC. Will let you know.

Posted by Martin Jones (Member # 1163) on June 25, 2015, 04:07 AM:

The EL84 by itself is the Exciter oscillator. The EZ81 is the power rectifier for the unit.
The other two EL84s are the audio power output valves, usually a matched pair when new. Try swapping each one in turn with the oscillator EL84 to see if there is an increase in Exciter lamp brightness or overall volume. If the amplifier gives you the result you need with a particular EL84, use that one. If no improvements are evident, put the valves back in their original sockets.... and look elsewhere for the solution. Don't ignore the possibility that ALL the EL84s are weak.... you could try a new one.

Posted by Terry Sills (Member # 3309) on June 25, 2015, 05:00 AM:

Martin
I changed the EF86 which is covered by an aluminium cover (shielded?) but no noticeable difference. However when I powered up I noticed that the ECC83 flared when first switched on, so I changed that and there was a noticeable difference in volume. Still not booming sound but with full volume quite audible. I would really like to get hold of a complete set of new valves as the ones I am using are all used and so I have no idea if they are weak or strong. Any idea where I can get good valves?

Posted by Martin Jones (Member # 1163) on June 25, 2015, 05:51 AM:

Yes. Go to ebay...... put in valve number... press Enter.

Simples!

Posted by Maurice Leakey (Member # 916) on June 25, 2015, 06:54 AM:

For valves, I always use Langrex.
http://stores.ebay.co.uk/langrex?_trksid=p2047675.l2563

Posted by Terry Sills (Member # 3309) on June 25, 2015, 07:13 AM:

Martin
Trouble with that is that you still don't know what condition they are. I don't have a valve tester so I would be reliant on the description. Not always a good idea with eBay and I may be in no better position to pinpoint the problem.
Thanks Maurice
I'll give that one a try.

Posted by Maurice Leakey (Member # 916) on June 25, 2015, 09:27 AM:

Langrex have been in existence for many years, long before the Internet. I have used them many times for projector amp valves.
They are always very helpful on the telephone. I was talking with them about twelve months ago when they told me that their entire stock has not yet appeared on-line.
They have huge stocks and the most popular valves are relatively cheap.

Posted by Terry Sills (Member # 3309) on June 25, 2015, 12:03 PM:

Maurice
Had a look - relatively cheap? You must have well heeled relatives! Lol. But you do get the assurance that they are not selling inferior valves.

Posted by Martin Jones (Member # 1163) on June 25, 2015, 02:29 PM:

Which is I suggested where I have usually bought any valves since the day I retired and foolishly threw away my stock of new valves in the stupid belief that I never wanted to see another one. I could be flogging them to you fellows now!

I've never had a bad one from any seller. If they are described as new they usually are. Many types are still being manufactured, as are new HiFi valve amplifiers for enthusiasts.

Posted by Terry Sills (Member # 3309) on June 25, 2015, 04:25 PM:

Martin
Foolish you certainly were. But who is to know the future. If we knew that we would all be millionaires. What I would like to know is what are the best valves - Brimar/Mullard/ Tungsram/Phillips - which???

Posted by Martin Jones (Member # 1163) on June 26, 2015, 01:42 AM:

There is really no significant difference in ANY of the makes you mention, they are all reputable names and produced valves to a very high consistent standard. My experiences over 50 + years using valves taught me that the make was not an issue when buying... the only consideration of any real significance was buying "power output pairs" as "matched pairs", but even that was not written in stone because quality control usually ensured that two new valves of the same type from the same manufacturer would be nearly identical.

Posted by Terry Sills (Member # 3309) on June 26, 2015, 12:22 PM:

It seems that some of the top valve names are now being made in Russia. Apparently the manufacturing equipment/machinery was sold to them and valves are now being produced at very competitive prices by Sovtec. I would imagine that they should be good quality if they are using our technology even though old.

Posted by Barry Fritz (Member # 1865) on June 26, 2015, 01:08 PM:

I looked into the Soviet made tubes several years ago. Based on statements from members of old radio forums and forums related to guitar amps, the consensus was that they are of good quality.

Posted by Terry Sills (Member # 3309) on June 26, 2015, 04:35 PM:

Glad to hear that Barry and they are a fraction of the price of what is being asked of British made originals.

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