Replacing a tube HV rectifier tube with a solid state one
 

This is a general question that i wanted to ask about. What are the pro and con's of replacing a tube hv rectifier with a solid state one in both a b/w or a color tv set? Is it recommended to unsolder the filament leads to use a solid state one if this were to be a permanent substitution?

These notes apply to all valve (tube) radios and TVs.

You get HT (B+) immediately with solid state, before the valves (tubes) have warmed up. This gives a higher HT voltage than normal for a short period which may overstress some components. You will usually need a surge limiting resistor in series with the solid state rectifier to limit peak current and get the correct HT voltage.

If the set uses series connected heaters then you will need to keep the original valve heater in circuit or replace it with an equivalent resistor. Otherwise the heater connections don't matter if you repalce with solid state. (In UK parlance filament is only used for directly heated rectifier valves - you won't find them in TVs very often)

Unless you have to replace a hard-to-find rectifier valve or have some other good reason for going solid state, them keep it original. Good reasons might include a transformer running near its limits where the power needed to heat a rectifier can be usefully removed. Or a set where the heat from the rectifier is having a bad effect on something.

:scratch2: Just curious , you say "hv rectifier" which usually refers to the high voltage applied to the CRT's screen , vs "LV Rectifier" which refers to the B+ that penguin mentions , which rectifier are you thinking of replacing , the HV or the LV ?

The HV rectifier such as a 1B3 in a b/w or a 3A3 in a color set.

The only time I replaced a 3A3 or so is when the filament winding was arcing through. I cut the leads short and taped them up, away from the transformer.
I told the owner that it's the cheaper way for the repair. If the set was old, it was the smarter move.

A good question, Tony. I've been playing with a set with flyback issues (replacement unavailable) and trying to find a way to nurse it into operation. I wondered if removing the filament windings would make enough difference to matter. And, if they aren't connected to anything are they still having an effect on the flyback?

They should not effect the flyback if disconnected. That assumes you mean disconnected from the rectifier socket. If they are still wired to the socket there one effect they could have: if one end of the winding is connected to HV (as is usually the case) and the wire insulation has broken down at a point it touches the chassis or is wrapped around the flyback the breakdown leakage can kill the HV level, load down the fly and even damage the rect.

I have had problems with filament windings connected to sockets with carbon tracks.
I simply disconnected them and shrink wrapped them, and used a solid state rectifier.
If the disconnected leads don't have a short in the transformer, they won;t have HV on them. But a short in the transformer could leave them with HV pulses on them.

These problems have been on cramped B&W portable sets.

Is there a direct plug-in solid state replacement for a 3A2?

I tried using SS rectifiers on sets with arcing filament windings. They can
be a PIA to change in some sets. I found them very unreliable, failing after a
year or less. Looked around & found some thin & very flexible high KV
wire & never used them again. The one use they still had was to mouse a
set to run for evaluation before putting in the time.

BTW for the beginners the 1-3 volt filament for the HV rectifier is sitting at
the HV level along with the tube, cup, & anode lead. Keep that in mind....

73 Zeno:smoke:
LFOD !

Here's a true story for whatever value it will offer. We had an RCA CTC11, and somewhere around the mid 60s, the picture tube went weak. Dad replaced the original sulfide tube with the later rare earth version and discovered shortly after that it started eating 3A3s every couple of months.

Dad replaced the 3A3 with a plug in SS stick (I believe International Rectifier made them) that the parts store was selling. That lasted a week. Dad got a warranty replacement and tried again, and the second solid state rectifier lasted until 1977 when the second picture tube went weak and the TV was retired.

But, there was no rewiring required with the IR rectifier, so we never removed the filament winding. It also apparently could handle more current than the 3A3 could. After the first failure, there was never an issue with the HV section of the CTC11 again.

John

You can only keep the filament wiring if it isn't arcing (which it sounds like it wasn't an issue in that CTC11).

When I worked in TV shops, an arcing filament winding was the only reason we ever used one of the SS replacements. Remove the filament winding, install the diode, and the set was fixed. Cheaper than replacing the flyback, or even rewiring the filament winding in most cases.

Otherwise, the SS replacements were considerably more expensive than a 3A3, 1B3 or whatever.

When using a silicon replacement for an EHT rectifier be aware that for some parts, the body of the part is too short to prevent arcing across unless it's potted. Heatshrink sleeving can also work, or putting several in series. They're very low cost now so that last apporach isn't as daft as it sounds.

For replacing a failed heater winding on the LOPT (flyback in US parlance) the inner core of some co-ax cable will often work. Ideally solid dielectric, not semi-air spaced.

My preference is only using a solid state replacement with a current limiter. Otherwise you'll hit your tubes with a surge of high current.