Spark on reverb transformer.

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psychepool
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Spark on reverb transformer.

Post by psychepool »

https://www.youtube.com/watch?v=9rLsCD- ... e=youtu.be

It's my diy tube amp based on Deluxe reverb and Rectoverb.
This clip shows the spark on reverb transformer.
Trans is hammond 1750A, the deluxe reverb replacement.

When I disconnect reverb tank and push up the gain(preamp volume), there's the spark occurs. It's react with guitar signal. It occurs at blue line.(the signal line : 12at7 2/7 pin)
But when I connect reverb tank again, the spark disappears.
At the low gain setting, there's no spark even if the tank is disconnected,

I have the same transformer at my lunchbox style dumble but there's no spark even the tank is disconnect.
Of course it is different amp, has different reverb schematic and less distortion.

Is it alright? Nothing matter with this?
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ToneMerc
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Re: Spark on reverb transformer.

Post by ToneMerc »

psychepool wrote:https://www.youtube.com/watch?v=9rLsCD- ... e=youtu.be

It's my diy tube amp based on Deluxe reverb and Rectoverb.
This clip shows the spark on reverb transformer.
Trans is hammond 1750A, the deluxe reverb replacement.

When I disconnect reverb tank and push up the gain(preamp volume), there's the spark occurs. It's react with guitar signal. It occurs at blue line.(the signal line : 12at7 2/7 pin)
But when I connect reverb tank again, the spark disappears.
At the low gain setting, there's no spark even if the tank is disconnected,

I have the same transformer at my lunchbox style dumble but there's no spark even the tank is disconnect.
Of course it is different amp, has different reverb schematic and less distortion.

Is it alright? Nothing matter with this?
Looks like some sort of break down in insulation when there is not a load on it, I would replace it. Alright......I wouldn't play any gigs in meth lab.....LOL

TM
sluckey
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Re: Spark on reverb transformer.

Post by sluckey »

Same thing happens to your OT when you wail away on the guitar with no speaker connected. It's called flyback.
psychepool
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Re: Spark on reverb transformer.

Post by psychepool »

ToneMerc wrote:
Looks like some sort of break down in insulation when there is not a load on it, I would replace it. Alright......I wouldn't play any gigs in meth lab.....LOL

TM
If it is a break down in insulation, why doesn't it happen when the tank is connected?


sluckey wrote:Same thing happens to your OT when you wail away on the guitar with no speaker connected. It's called flyback.
So then, is this spark a normal situation?
No need to replace the reverb transformer if I load the tank to the trans?
The reverb itself is OK. It runs very well.

I need to check the reverb trans of my dumble amp. I often use it with no tank loaded. But I never saw or heard the spark at all.
But it's reverb is located at post master volume. I never set it to preamp/master volume at 10.
I will full-crank it and check the same thing is happen.
sluckey
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Re: Spark on reverb transformer.

Post by sluckey »

That spark may damage the transformer. I would not do what you are doing.
tubeswell
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Re: Spark on reverb transformer.

Post by tubeswell »

psychepool wrote:
ToneMerc wrote:
Looks like some sort of break down in insulation when there is not a load on it, I would replace it. Alright......I wouldn't play any gigs in meth lab.....LOL

TM
If it is a break down in insulation, why doesn't it happen when the tank is connected?


sluckey wrote:Same thing happens to your OT when you wail away on the guitar with no speaker connected. It's called flyback.
So then, is this spark a normal situation?…
No the spark is not normal. It is showing that the transformer winding insulation has already started perishing. If you keep doing what you're doing, you'll have a spectacular failure of the reverb transformer, and probably also taking out some other components in your amp.

You need to fix it by putting in a new reverb transformer. You can't repair the old RT - its not worth trying. If you have flyback sparks on one part of the winding, you may also have some in other parts you can't see, and also possibly even between the transformer core laminations.

Flyback deterioration is a permanent condition - it doesn't get better with time. Flyback voltage spikes burn a new current pathway through the OT, and once its there, its there permanently. Even now, continuing to use the RT, even with a pan/load connected, is no guarantee that you will not get catastrophic failure. The RT is already compromised.
He who dies with the most tubes... wins
psychepool
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Re: Spark on reverb transformer.

Post by psychepool »

sluckey wrote:That spark may damage the transformer. I would not do what you are doing.
Thanks sluckey.

I already heard that it's dangerous to power on with no load, but I forgot the reverb transformer is also a output transformer.
It's first time to see the result, and it reminds me the danger.


tubeswell wrote:No the spark is not normal. It is showing that the transformer winding insulation has already started perishing. If you keep doing what you're doing, you'll have a spectacular failure of the reverb transformer, and probably also taking out some other components in your amp.

You need to fix it by putting in a new reverb transformer. You can't repair the old RT - its not worth trying. If you have flyback sparks on one part of the winding, you may also have some in other parts you can't see, and also possibly even between the transformer core laminations.

Flyback deterioration is a permanent condition - it doesn't get better with time. Flyback voltage spikes burn a new current pathway through the OT, and once its there, its there permanently. Even now, continuing to use the RT, even with a pan/load connected, is no guarantee that you will not get catastrophic failure. The RT is already compromised.
Oh, it should be considered the RT is dead. I'll order and replace new one as soon as possible. thanks!
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jjman
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Re: Spark on reverb transformer.

Post by jjman »

Looking at a scheme I never thought that this is the same as an OT, as mentioned, regarding flyback. Why have the internets not warned us on this like with that other tranny?
If it says "Vintage" on it, -it isn't.
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trobbins
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Re: Spark on reverb transformer.

Post by trobbins »

Reverb driver is typically an SE amplifier output stage, so normal methods of over-voltage protection for the reverb output transformer apply.

Simplest protection imho is a MOV across the primary winding. That is likely to restrict the plate voltage to under the arcing initiation voltage that is presently being observed, and hence you could continue to use the same reverb transformer with no consequence (but obviously avoid using the reverb circuit when no tank is loading it).

Arcing could be just adding a carbon deposit along a creepage path, making it progressively easier for an arc to initiate, or provide a permanent residual current path (but that is likely to open up if current gets too high). The carbon deposit may include charred insulation, which would get worse with continued arcing. If the transformer did have a permanent current path, then given the video, it may be possible to take off the bellends, and physically scrape off any burn track and recover the transformer.
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