Hi Roger

Just checked p21 to the centre wire and there is continuity.

As it is affecting the Mhz section looks like I may still have a joint of track problem.

Excuse my ignorance but are these common cathode or common anode displays.

Just in case I have to get a replacement.

Off to bed now as it is 2AM here, been at this all day.

Kind Regards

MikeG3ZCC

Hi Roger

Just checked p21 to the centre wire and there is continuity.

As it is affecting the Mhz section looks like I may still have a joint of track problem.

Excuse my ignorance but are these common cathode or common anode displays.

Just in case I have to get a replacement.

Off to bed now as it is 2AM here, been at this all day.

Kind Regards

MikeG3ZCC?

Hi Roger

Just seen your reply.

Looks like the problem now is with segment a the top one.

All the others are working.

Will check that centre wire tomorrow.

Kind Regards

Mike

G3ZCC

Hi everyone

Well after a day checking those three pins, fitting? 5mm blue LED's to the PTO and meter, fitting it all back together still a problem.

looks like segment a if I read the schematic correctly.?

Back to the drawing board.

Kind Regards

Mike
G3ZCC

Hi all. Thanks for the fine info and offers.? The original plan was to use an old Heathkit unit I had? but? I've managed to obtain a 2-BQ with one fitted.
So the connector is no longer required.
Regards
Gary ZL2AKI

<Hmm... They survived through three engineering generations and served the purpose over the decades of real world use. Real HV fuses are expensive for a new build. Even the great W8JI <espouses the use of fault limiting resistors, although he prefers higher values.

<73

<-Jim
<NU0C

##? ?You won't see any amps other than drake, using a .82 ohm? @? 2 watt? resistor.....for a... 'hv? fuse'.? ?New, correctly sized? HV? fuses are cheap, and meet? ?UL /? CSA? standards.? ?Drake could have bought thousands of em? at whole sale prices.? ?W8JI? typ will use 10 ohm,? or? 20? ohm max, for the? current limiting resistor (aka...'glitch resistor').? ?ARRL handbook? sez to use? 10-15 ohms? per KV.? ?After building? 38? x hb? B+? supplies over the years, and experimenting with different value glitch resistors,? I settled on? 50 ohms, regardless of the? actual? B+? value.? ?But it's a two edged sword.? ?Higher values will limit fault current to a lower value.... BUT dissipate more heat, depending on? mode, and how much average plate current involved.? ?Higher value? glitch resistors? also have a higher? V drop? across them...? ( which will increase even more, with higher plate currents).?

##? In? L4B? size amps,? ?with say? 2650 vdc no load..and a fault occurred,? it's then just 2650 /? 50 ohms =? ? 53 amps of fault current.? And? ?53 amps of fault current will open off that? BUSS? 750 ma HV fuse in? < 2 msecs? every time.? ?On a L4B, with? 800 ma peaks on? ssb,? the? V drop on peaks is .8? X? 50 ohms? = 40 vdc? V drop on the loaded? B+.? ? Average plate current on ssb mode is? typ? 400 ma( with processing).? ?(.4 X.4 )? ?X 50 ohms =? ? 8 watts dissipation? in the? 50 ohm glitch R.? ?( and? 32 watts if a? 800 ma? dead cxr, like tuning up with a cxr).? ?Hence my use of a? simple? 50 ohm, 50 watt wire wound? for the glitch? R.?

##? On the bigger? HB? B+? supplies, with a lot more filter C,? ?I use globar type AS? resistors.? The? AS types are designed for glitch service, and will handle a lot of joules of? energy...and also a lot of HV.? Typ,? 4 x 200 ohm, type? AS? resistors are wired in parallel..and also fan cooled.? ?But that's what's required for 5-8 kv dc? supplies..and tubes that? suck 1.5? to 3 amps of plate current.? ?3 amps? ccs? into 50 ohms? =? ?450 watts, which is a bunch.? The type? AS? resistors are? 18"? long x 1.5"? diam,? rated for? 225 watts each /? 900 w? total.? They run hot when used in ccs modes.? ?Lower? duty cycle modes like? ssb is a non issue,? only? ?1/4 the? dissipation...same as? the 50 ohms used in the? L4B? B+? supply.

Jim? VE7RF

That’s the term I was looking for, fish paper.

Drake may not have widely implemented that ECO but I have had several TR7’s that did have it and I installed it on every one that came through here. It is a tight fit and the results of that short are not leading to a happy ending. If the short is short-lived, you only lose the segments but a longer-term short will destroy the display. No down side to doing this, big downside to not doing it.

Gary. W0DVN

On Mar 21, 2021, at 11:15 AM, Jim Shorney <jshorney@...> wrote:

?
Interesting. I don't recall having seen this. Fish paper maybe?

73

-Jim
NU0C

On Sun, 21 Mar 2021 11:00:19 -0500
"Gary Follett" <xntrick1948@...> wrote:

Drake, in later radios, glued a grey piece of high voltage cardboard on top the PTO assembly. Your radio looks like a pretty early one so may not have this.

Hi Fred?

I was going to buy a TR7 back in the day, got warned off, spent more money and bought a Triumph Stag.

After three engines I sold it and bought a Lotus Sunbeam.

Best car I ever had,

Kind Regards

Mike

G3ZCC

Hi Roger

Thanks for that, I just checked and looking at the board from the front, there is a bad solder joint on the left wire link of the three.

Just resoldered it, it came off in my hand.

Fitting some blue LED's to the meter and PTO today replacing the two bulbs, cant wait to check the DR7 out after everything is all back together.

Kind Regards

Mike

G3ZCC??

开云体育

Murch did not try to claim it was his design but was a copy of the Ultimate Transmatch? by Lewis McCoy.
Murch just put it into production and there were several versions of it over the years.
While I am not sure, I think Murch made many of the components as they were hard to find.

Ralph ku4pt






On Sunday, March 21, 2021, 04:03:48 PM EDT, Steve Bookout, NR4M <steve@...> wrote:

None of us know everything.?‘Murch’ is an old school brand of basic, well built, tuners.?
Much better, and beefier than many current tuners.?
73 de Steve, NR4M?


On Mar 21, 2021, at 3:57 PM, Billy Pickering KO4INE <pickeringw@...> wrote:



?It's another brand of antenna tuner made by Murch Electronics.
_._