Flyback for Admiral 20A7
 

Hello folks of Videokarma,
In my small TV collection, I have 2 tube TV's but none are working anymore.
The dreaded flyback issue... :mad:
I want at least one tube TV working in my collection!

These times, is becoming extremely expensive to acquire a tube TV, since most people loves old furniture, and old TV's in general have beautiful cabinets (I assume that people discard the ugly ones ;) and prices are on the stratosphere (or shipping, due to weight, or both). Or, if is cheap, have missing parts, or with some vital part damaged (tube, flyback...)

I'm trying to find a compatible part, but without success.
For the Admiral TV, model 20A7, I don't have the part list of this model. The actual flyback has a code on it: 15A1248-2, but I suspect that is one replacement part and not the original one.

I'm motivated to even change the H circuits on this TV (or the Telefunken) if I find one flyback compatible with it's yoke (20mH total inductance for H part), or if I find a flyback + yoke compatible with 23" 110° CRT. No need to match the V part; I can adapt the circuit if I need. If differences on auxiliary circuit exists, is only a matter to wind some wires externally.

I see a lot of flyback and yoke models on the Early Television Foundation, but I don't know a guide for matching flyback, yoke and CRT.

Any advice about compatible flyback for these conditions (original, compatible or for changing circuits) will be greatly appreciated!

The number on the FBT looks to be the correct part number.
Its in the format Admiral used till the end.
Manual is Sams #532-1 that will give you the part number and
often substitutes from Stancor, Thordason etc.....

73 Zeno:smoke:
LFOD !

It's worth getting your own copy of the Sam's, but if you need someone to check if Sam's lists generic subs sooner than that I could look that folder up and post the numbers I find.

If it's possible for you to check, I really apreciate it!

Thanks! I'm able to locate the manual with exactly these number on eBay.

According to Sam's the flyback (Transformer T4) has Admiral part numbers 79E77-9, 79B77-9(used in production runs 10 and 11), and lists Merit HVO-185, Stancor HO-318, and Triad D-194 as subs.

It also lists an alternate flyback under Admiral part numbers 79E77-13 and 79B77-13 with no after market subs listed. This part was used in production Run 12 of this chassis.

Admirals usually had production run numbers stamped on the back of the chassis.

The Sam's is dated May of 61 BTW so it's probably a 1961 model year or a late 60.

I checked the Thordarson cross ref and it lists FLY-176 as a sub for the -9, no sub for the -13 used in run 12

Thanks all! I already ask some vendors about these part numbers. Maybe I have some luck... :)

Production run...
 

Ohhh... :o in my haste, I forgot to check if the chassis is exactly the same code from USA. This TV is assembled here in Brazil, and although it have a lot of USA-Admiral parts including capacitors, is better to be safe and verify. I assume that the serial number grouping is obviously different here.

If is possible to someone to check the following, will be of great help:

I included here the local schematic (the HOT sector) to see if corresponds to a HOT xx-9 or the HOT xx-13 (or worst, if is a different unrelated chassis***).

***only because of this, I don't purchase the SAMS manual yet. If is the same family chassis, I will buy ASAP.

If you do order a Sams try to find the original paper
copy. Sams charges too much & all you get is a crappy
PDF or Xerox. Originals are HIGHEST quality.
Sams only covers US sold models, not even Canadian.
Other sets I have seen were based on a US chassis & usually
look a little different. They were sold as kits then assembled
locally with some local parts used.

73 Zeno:smoke:
LFOD !

Adventures with Admiral...
 

...since is 100% sure of flyback being damaged, I removed it from chassis, and discovered the real code from it. I assumed being the 15A1248-2, but is a code for the support, and forget to see the other side... the code is really the 79E77-9, from American chassis run -10 or -11, like Electronic_M said.
Here in the thread, Tim suggested the FLY-176 as a sub, and recently I found this link: https://archive.org/stream/Thordarso...-1965_djvu.txt . Is very difficult to see the messy text, but confirms the FLY-176 as a sub.
Well, a month ago I contacted some people about this part. Only Moyer company responded that have a FLY-176 (the others don't have any compatible part), but then I not received response anymore... maybe they sell for a local client meanwhile, or some error in the catalog, who knows.

But anyway, since I suspect about the flyback secondary being the culprit about frying the part, I simply started an experiment: I removed the secondary entirely (and it shows signs of overheating), and connected a tripler directly to anode from 6DQ6. Normally we have a 4.5kV pulse here, so it translates to ~13.5kV to final anode, sufficient to work. Better will be a quadrupler, but then is needed to regulate voltage for not being >20kV.
With the absence of secondary, the tuning changes. I used a bench PSU for slowly watch the resulting +Boost voltage and the final voltage (using a color TV focus divider as a HV probe), and applying capacitors in parallel with yoke for compensating the tuning. Without any cap, the HV skyrockets and 6DQ6 arcs internally, and sweep is too narrow. A compromise was found, like I show in some photo here (small due to small maximum size here). I'm able to see a image!!! Hoorray!! (vertical not adjusted; more on this later).
A compromise between image line maximum size and is here, since one motive for high secondary pulse is the leakage inductance between primary and secondary, and with this process, this is absent. Too large a image horizontally, and HV downs too mutch, for example.
...but flyback starts to fry if I push it higher than 120mA cathode current, so I assume that the primary suffered some damage also. With 100mA it remais stable. At least it not smoke anymore...

This crazy experiment is motivated due to extra rarity of theses parts.

In fact, due to problems also with vertical with Admiral, I used the Telefunken to generate the vertical (and video signals); I only used the H sweep from Admiral for testing. The H and V yokes from Telefunken are radically different, so the V sweep suffered a little (at least good enough for testing). I only will invest time with Admiral if I find the flyback, or the tripler/quadrupler experiment works adequately.