14rp4 substitute
 

Does anyone have an substitute book for crt tubes. I have a 14rp4a for an admiral and I would like the reading to be higher so I may be looking for a sub. Would a 14atp4 work or what would the differences be.

These are the CRTs that will sub with no mods needing to be done,14RP4,14NP4,14NP4A and 14SP4. All the best,Tom.J

The 16" version of the set, 26R12 I think, used the same series of tubes, 16RP4, 16TP4 if memory serves me. Try "Googling" those numbers and compare the tubes.

Check the info above, it arrived whilst I was typing.

Any chance a 14atp4 would work ?

Short answer NO, the 14ATP4 has no sub. Sorry, Tom.J

Hmm, I wonder what is so different , it looks the same along with the gun.

The difference is the the heater current and voltage. 8.4 volts@ 450ma.
These tubes were used in RCA's and Westinghouses with 450 heater string, 17DQ6, 17AX4 etc.
A 50 ohm 2 watt resistor in parallel with the 14at heater would work OK.

The 14atp4 I wanted to use in place of the 14rp4 and I'm not sure what your saying with the resistor. Are you saying to put in the 17ax4 and 17dq6 in place of the 12dq6 and 12ax4 and then this raises the heater voltage and use a 50 ohm 2 watt resistor between the heater. I'm probably way off here thinking the 17, volt tubes would take more .im missing something on how to get more voltage for the crt . If the physical size is the same as the 14rp4 I could just use a separate heater transformer for the 14atp4 , that should work.

Timmy, dieseljeep is saying that the heater current of the 14ATP4 is different than the crt you have in your set. If you do what dj says you put the 50 ohm 2 to 3 watt resistor across the 14ATP4 heater only, that combo makes the current draw of the crt resistor pair 600 ma. to match the current draw of the rest of the tubes in the set. If I did the math right a 24 ohm 3 watt resistor will be just right for the crt shunt resistor. Tom.J

So what is being said is I would be able to use the 14atp4 provided I put the resistor across the heater. I looked at the size of both tubes and if I didn't miss anything it looks the same maybe a 1/6 inch different which I should be able to make that up if that's the case. The heater voltage would be enough 6.3 v aside from the 8 volts the 14atp4 requires.

What is the model number of the set? Does it have series string heaters or is there a power transformer supplying 6.3 volts to the tube heaters?

jr

The chassis number is 14yp3c . I would just like to know if that tube will fit and I can use it.

Ahhh! series string, so the 14ATP4 with heater bypassed with the correct resistor will get the proper 8.4 volts.

jr

If the crt you have will fit yes you can use it as long as you use the before mentioned shunt resistor. Make sure you make note of the change and note the added resistor for the crt heater in your notes for future use. FYI you have to take in account not only the heater voltage but also the heater current as well, a mismatch in current is not so good for the tube(s). Tom.J

So just putting the resistor across the heater will enable the 14atp4 tube to work. Now I'll have to double check to make certain that the measurements are really close or the same. Well it looks like the 12atp4 overall length is around 3/4 of an inch smaller ,bulb diagonal is the same , screen is 12 1/6 x 9 1/2 as opposed to the the 12rp4 is 12 1/8 x 9 5/8 . How does this look, slight mod maybe to fit the same as the other, what would you decide, chance it ? It is very close.

My last entry just cited the tubes that would be in a set that used a 14ATP4 crt. My calculations still show the resistor to be 42 ohm, 3 watt resistor across the 14AT heater.
I just mentioned a 50 ohm, as it's a more common value and will shunt 7.5 volts, kind of a happy medium.
Current in a series circuit is constant and the slight increase will balance out.

Timmy as far as the ATP4 crt fitment you will have to try it to see, we can't do it for you it's up to you to try it and go from there. Dieseljeep bud you and I, both got the resistance value wrong for the tube in question 8.4 volts not 6.3 volts makes the resistor a 56 ohm not 42 or 24 ohm. 3 watt rating still is fine. Went back and checked the tube specs again and saw the mistake, sorry about that. Tom.J

Just out of curiosity wouldn't it be safer to just use a separate transformer for the heater and place a resistor in place of the crt to complete the string ?

Yes you could, finding room on the chassis mite be a bit of trouble though. Finding a transformer with a 8.4 volt at 600ma rating mite be hard though. Remember set makers used shunt resistors all the time till the art of tube making got to the point where their were standardized current draw for all tubes. Tom.J

A while back, someone wanted to sub a 14R for a 14AT. There, the transformer was the only way to handle that problem, plus a 6.3 volt transformer is a common part.
In that set, there was enough room to mount the transformer.

Well if I go with a transformer I have to find at least an 8 volt 4 - 8 ma which may be hard to find.

Just follow the proceedure that that everyone seemed to recommend, a 42 to 56 ohm resistor @ 3watts or so.
It's not like you're dealing with a 3KP4. :scratch2:

I have an odd question, how does putting a resistor across the 6.3 heater source give 8.4 v and more ma ?

An odd question, how does placing a resistor across 6.3 v heater source give 8.4 v with higher ma ?
Don't know why it posted twice....

Using a 450 ma heater in series with 600ma tubes without a shunt resistor, the 450ma heater would receive too much voltage and the 600ma tubes would be starved. You could consider the 450ma heater as the weak link.
Once in a while, an experiment is in order!
When installing the CRT, try various resistor values between 42 and 56 ohms and check the voltage across the heater. Line voltages vary in some areas.
Get the set working properly first, with the original CRT and then address the CRT issue. :thmbsp:

So in the end the 14at will be getting 6.3 v or around 8 v . I get the ma but not the voltage. Just had a thought the B&W tube brightiner they increase voltage to but the ma may be low, any thought on these in this case.

A series heater circuit is constant-current.

Parallel heater circuits are constant-voltage

So in a series string, the tubes' heaters have to be rated for a constant current. Therefore different voltages appear across different heaters, leading to oddball voltage designations (e.g., 2AF4, 3CB6, 5GH8, 19AU4, etc. etc.)

In a parallel circuit, the heaters all have the same voltage but some have different currents.

Ok so this admiral is recapped and have sound and close to 9kv for hv and the b+ is around 10 volts less then it should be however I have no raster at all the video tube tests good, any ideas .

Is your current tube meant to use an ion trap, and if so is it on and adjusted properly?

What are your gun voltages and what does the service manual say they should be?

Those are the first questions I'd ask myself in your shoes.

Ok I have no voltage on the board that is supposed to have 255 v . The schematic shows the diodes with the line on it so I'm asking that line, is it the line band on the silicone diode ? I have always had a brain fart when it comes to that band on the diode. The schematic shows + and - so the would the minus be the band on the diode . What may have me messed up is the schematic shows the line as positive but the diode band is negative so I have voltage but no voltage at the cap that feeds the IF board 255 v I thought befor the voltages were there but I was wrong.

The stripe on the diode schematic symbol is the same as the stripe on the physical diode you install...It is the cathode and is counterintuitively marked with a plus on old seleniums (since B+ returns to the cathode of the diode).

https://upload.wikimedia.org/wikiped..._en_fr.svg.png

https://en.wikipedia.org/wiki/Diode#...nductor_diodes

To get the equivalent 8.4V you could use a 12.6V transformer and a series diode (no filter cap) with the CRT heater. The heater will heat up the same with 8.4VAC or DC.

Or you could rectify 6.3VAC with a filter cap to get 8,4VDC to run the CRT heater.

You might be able to use a CRT brightner in "parallel" mode. These used small transformers to produce around 8VAC from 6.3VAC. In the series string you have, the transformer may make the CRT heater at 8.4V@450ma look like a load of 6.3VAC@600ma.

So then the + marked on the selenium would be the end of the diode not marked, would I be correct ? Because on the schematic it shows the cathode mark as positive so if that's a typo then I have them backwards.

I think they used to mark the terminal with a "+" that you get B+ from when AC is applied to the other terminal.

Here is a good link to an article describing how to replace selenium rectifiers with silicon rectifiers.

http://w3hwj.com/index_files/RBSelenium2.pdf

The + mark on a selenium is simply saying "the B plus comes out of here.":deal:

Ok, I'm confused, it looks like I have the diodes right but I'm not getting 255 v from c2 and c3a both are 300 v rated caps at one point it was there then gone. Strange as it sounds, both caps are grounded to chassis which is one side of the ac in the other ends go to the terminals I broke off the old cap never removing any wires this is why I thought I had the diodes wrong. I reversed them and burn the ac input resistor so I put a new one in after putting the diodes back so I'm thinking is it possible to have one diode reveresed, then how to figure out which one but it seems if I change one it will short against the other.

Do the diodes check ok? how about the input cap(c1) ? These components may have been damaged when you burned out the input resistor.

jr

I'll see if I can describe the proper connections verbally......

Connect the unbanded end of M1 to the chassis ground. Connect the banded end of M1 to the junction of the + end of C1 and the unbanded end of M2. Connect the banded end of M2 to the junction of the + end of C2 and L10.

Be sure to check the caps before you energize the circuit.

I know the manufacturers of the selenium rectifiers meant well, but their "+" designation is just counter to standard schematic documentation.