Duncan's 1960 Magnavox

[Mr.Duncan]

Today's the day!

Finished replacing the last multi sectional capacitor.

The old one was VERY swollen and leaking fluid.

I powered the set up slowly with a variac.

At full voltage I'm pulling 2.5 amps which seems to be normal. No abnormal sounds, no arcs.

The photo below kind of exaggerates how bright the tube filaments are glowing. Much more mellow in person.

I'm getting just a non-adjustable horizontal line across the screen.

So I'll need to do some reading as I have no clue what controls the vertical movement of this line?

**I only ran the set for about 30 seconds with the screen set to minimum brightness** - didn't want to burn the CRT.

PXL_20240806_221113960.PORTRAIT by Thomas Duncan, on Flickr

PXL_20240806_225509131 by Thomas Duncan, on Flickr

PXL_20240806_230959278 by Thomas Duncan, on Flickr

PXL_20240806_230953330 by Thomas Duncan, on Flickr

The safety glass in the display makes the line look much thicker than in person.

PXL_20240806_225528496 by Thomas Duncan, on Flickr

[Mr.Duncan]

Upon checking both these tubes, one BARELY shows good on my tube tester.

6BF6 - Pass
Vert OSC & AGC

6DT5 - Fail? - Readings are poor.
- Labeled as VERT output.

Photo of 6DT5 test below.

PXL_20240806_234132521 by Thomas Duncan, on Flickr

PXL_20240722_010820973 by Thomas Duncan, on Flickr

[kvflyer]

A vertical output tube can cause the collapsed raster that you show but I would be looking more at capacitors in that section first.

[Mr.Duncan]

Originally Posted by kvflyer

A vertical output tube can cause the collapsed raster that you show but I would be looking more at capacitors in that section first.

Will do! All the small capacitors were replaced, new capacitors were checked before & after install.

I see that the old multi-section can C2 capacitor was in circuit with the Vertical output tube. And that capacitor was leaking fluid/swollen/ejecting a black foam type material?

[Electronic M]

Marginal tubes can cause issues like lack of oscillation, but usually there should be some deflection especially if you had deflection before the recap.
Recheck your work in the vertical circuit and make sure you didn't install any end of any vertical stage cap to the wrong terminal in the set. Also check B+ voltages to the vertical. If you lost a power supply rail that feeds the vertical that could cause no deflection too.

One thing you can do as a troubleshooting measure on a transformer powered set like that is connect the grid of the output tube to the heater line with a .1uF cap and see if you get some deflection.

[Mr.Duncan]

Originally Posted by Electronic M

Marginal tubes can cause issues like lack of oscillation, but usually there should be some deflection especially if you had deflection before the recap.
Recheck your work in the vertical circuit and make sure you didn't install any end of any vertical stage cap to the wrong terminal in the set. Also check B+ voltages to the vertical. If you lost a power supply rail that feeds the vertical that could cause no deflection too.

One thing you can do as a troubleshooting measure on a transformer powered set like that is connect the grid of the output tube to the heater line with a .1uF cap and see if you get some deflection.

Will check tonight an update.

I forgot to mention the whole reason I'm re-capping this set is the C2 4 section capacitor did blow out (overheated, swelled up, and popped) - causing loss of picture. The whole process took 2 seconds, and I shut the set off while the cap popped.

Looking at the diagram 6DT5 tube is connected to one section of C2.
(20uF Square) - I assume when C2 blew out, it could have damaged that tube.

I'll dig more into it tonight.

tube by Thomas Duncan, on Flickr

[jr_tech]

WAG...perhaps R-50 opened when C-2 blew.

jr

[Mr.Duncan]

So far all replacement capacitors and old resistors are testing fine, and are in the correct locations.

I'll dig into it more tomorrow to double check as I'm getting a bit tired.

I did notice on 6DT5 that pin #8 (empty) was barely touching pin #7 wires.

Not sure if that had to do anything, I bent it out of the way.

PXL_20240807_223523011.PORTRAIT.ORIGINAL by Thomas Duncan, on Flickr
image by Thomas Duncan, on Flickr

[Electronic M]

Unlikely C2 damaged the output tube, but R50 that JR Tech mentioned could easily have been damaged if there was excessive leakage or shorts on that section of C2.

[Mr.Duncan]

Originally Posted by Electronic M

Unlikely C2 damaged the output tube, but R50 that JR Tech mentioned could easily have been damaged if there was excessive leakage or shorts on that section of C2.

I agree, so far R50 and R51 tested fine. But I may replace them just incase.

R50: Measured 232. Spec is 220
R51: Measured 328 Spec is 330

[MuzzcoVW]

I'm really enjoying following your journey here. That set is a copy of a unit I was looking at in NY state... but was about $2000 overpriced. I'll be following along as I begin the recap of my Silvertone this weekend. What CRT does that use? It's the same size as my Silvertone. Oh, and someone said they wished they had an electronics parts hous like that nearby... same here!

[old_tv_nut]

Originally Posted by Mr.Duncan

I agree, so far R50 and R51 tested fine. But I may replace them just incase.

R50: Measured 232. Spec is 220
R51: Measured 328 Spec is 330

In my opinion, replacing common resistors that are in spec "just because" is a waste of time if you have operational problems that you need to get fixed, unlike certain capacitors that could be eventual failure points.
Did you know that 10% or 20% carbon composition resistors were often near the plus or minus limit of value because the production line output of a particular value covers the whole range of +/- 20% and then the 5% parts are selected, and then the 10% parts are selected from the remainder, and then the over 20% parts are culled from the final remainder? So old tube-era sets were expected to have resistors that are towards the ends of the spec and still work. The time to replace resistors "just because" is after all the real problems are fixed.

[Mr.Duncan]

Originally Posted by MuzzcoVW

I'm really enjoying following your journey here. That set is a copy of a unit I was looking at in NY state... but was about $2000 overpriced. I'll be following along as I begin the recap of my Silvertone this weekend. What CRT does that use? It's the same size as my Silvertone. Oh, and someone said they wished they had an electronics parts hous like that nearby... same here!

Thank You!

This one uses a 24AHP4 tube.

[old_tv_nut]

This question of resistor tolerance reminds me of the question of whether the major brand TVs were actually better quality than second tier. In terms of component tolerance the answer is yes, since the high volume of Zenith or RCA meant that they could get parts cheaper. At Motorola, standard practice was to use 10% resistors in designs unless 5% was absolutely necessary, while Zenith used 5% as the default until analysis showed 10% would not reduce final yield. When I moved from Motorola to Zenith I was surprised to find the lab stocked with 5% resistors instead of mostly 10%.

[Mr.Duncan]

Originally Posted by old_tv_nut

In my opinion, replacing common resistors that are in spec "just because" is a waste of time if you have operational problems that you need to get fixed, unlike certain capacitors that could be eventual failure points.
Did you know that 10% or 20% carbon composition resistors were often near the plus or minus limit of value because the production line output of a particular value covers the whole range of +/- 20% and then the 5% parts are selected, and then the 10% parts are selected from the remainder, and then the over 20% parts are culled from the final remainder? So old tube-era sets were expected to have resistors that are towards the ends of the spec and still work. The time to replace resistors "just because" is after all the real problems are fixed.

I think I may go that route "just because" once I solve the vertical circuit problem. I'm still struggling to find the error, so far all replacement capacitors are wired correctly & test correct.

When able, I've been buying higher spec replacement parts.

For example if it called for a 20% +/- tolerance I'd replace it with a 10% tolerance part capacitor. (plus slightly higher voltage rated capacitors 400 vs 630.)

As for resistors, that does make sense!

If we look at R50 for example, it should be 220 ohm @ 1watt.

Does anyone have a recommendation of what TYPE to buy?

When looking at that spec resistor with a 1% tolerance rating I have Wirewound vs Metal Film.

If I go to 5% tolerance "Metal Oxide Film" shows up.

What's best? - I really don't mind paying extra for higher quality / better parts.

options by Thomas Duncan, on Flickr