modernizing?

[Rodzilla]

while waiting on more parts and a new speaker to arrive[the old one works ok,but has some issues with voice coil alignment as well as a few small holes and previous patches that the cone's extreme fragility makes me reluctant to even attempt to fix]

in the meantime I've started on the cosmetic side..the "bronze" trim is indeed brass,and as was suggested earlier,it's not actually bronze plated but has some kind of tinted lacquer applied...some brasso and a little elbow grease quite nicely took the badly deteriorated finish off the large trim piece below the dial,that cross piece is now gleaming clean brass...i guess the question now is,being that i rather like the bronze look,what can i find to duplicate it?tinted lacquer is not something i see at wally world or home depot...

[Bill Cahill]

What makes you think it's tinted lacquer? It's not. It simply has decayed with age. It happens. Takes longer than no lacquer at all, but, it still happens.
Bronze plating was done with special acids, and, other chemicals. Difficult to duplicate.
Bill Cahill

[Rodzilla]

Originally Posted by Bill Cahill

Bronze plating was done with special acids, and, other chemicals. Difficult to duplicate.
Bill Cahill

i suspect it was spayed on as it came off very easily...once i had determined that i wasn't going to try to save it as it was,i could actually scratch off the "bronze" with my fingernail,it was not metal plating...I'm pretty sure it was lacquer or maybe some other type of coating.but it was definitely not real bronze...the brasso reduced it too sludge and had it down to the bare brass in a matter of a few minutes...

as i mentioned near the beginning of this thread...the real deal can be done.I'm not sure of the quality of the results,but like most things these days...if you can dream it up,it's on the web...as i said I'm not sure of results one can get from these systems or of my due diligence in the polishing and cleanliness that's absolutely required for a decent result in ANY plating process...but it SEEMS easy enough.unless there turns out to be an easier way to replicate what was there...i may give it a whirl

http://www.caswellplating.com/kits/index.html.

[Reece]

Are you sure the trim is solid brass? Could be brass plated steel. Test with a magnet. No matter, if the finish is shiny brass "looking," look in a crafts store for "stained glass" spray lacquer. Some have used an orange tint of this stuff to make brass (or even shiny steel) look more like an antique brass.

[Rodzilla]

yup it's brass,tho "solid" is probably misleading,it's formed brass channel for the main cross piece,the logo is actually solid cast brass..its non magnetic and the real tipoff was the hint of green corrosion on the backside ..even the knob brights cleaned up similarly..tho I'm not sure of their actual composition...and you've read my mind on the crafts store,was thinking that just last night,there's a large one i've not been in,that i need to check out

[Rodzilla]

i think i have a plan on the brass,but i'm gonna wait till last on that...but by way of an update on this project

i had ordered a new 19t8 and 12at7 for this radio since they were the only tubes that didn't test near new. i was hoping that possibly the new 19t8 MIGHT do something with the slight buzz,since i'm about out of ideas and even theories at this point to solve it.... as well before i started messing with oscillator coil spacing that has existed for some 60 years,in order to fix the slight offset in the dial like the service info instructs,.i figured i'd get a new 12at7 and see if that affected anything there..both tubes work out to about a 20 dollar experiment,and i figured I'd at least know that all the tubes were then tip top even if it affected no change at all

other than these issues the set has been performing well enough,i find the heat from the 50l6 a bit worrisome but being that it seems to be operating on proper voltages,if not actually even a bit on the conservative side,i guess thats just the way it is...it gets warm enough on top that plastic would surely soften and warp,but i guess the bakelite can take it....??and i guess i know where to set a cup of coffee i need to keep warm

anyway i've had the thing playing off and on for a while now,and for a good while last night with good volume and sound quality,no issues whatsoever beyond those i've mentioned,so i shut it down for a while and when i came back later...dead,the dial lights up,but no sound...damn,a quick look inside revealed no lit heaters on the tubes...double damn,now of course in a perfect world the filament that went would have belonged to the 19t8 or 12at7 that i had on order,the ones that actually arrived just today...but nope,after checking across the heater pins of the four other tubes...I've lost a perfectly good testing 12ba6 to an open filament...dang setback #112 on this project,i got new tubes to put in,some stuff to try and i can't fire it up until i locate a working 12ba6 lol

[Reece]

Go to a heating/AC contractor and ask them for a scrap of ductboard, all you need is a piece about 3 x 4 inches. They will have a dumpster full of it. Ductboard is a compressed fiberglass material with a foil facing. It's an inch thick. Use a long knife and slice through so you have a piece about 1/8 of an inch thick with the foil face on it. Glue that inside the top of your radio with the foil facing down towards the hot tube or tubes. Cooler top.

[Rodzilla]

ok i give up...the thing has a buzz,will always have a buzz,and probably always did...i don't know what else to try short of replacing every single component and rewiring the whole chassis...and I'd lay odds it would STILL buzz!

can anyone add ideas to this list...

caps are done...all except the couple hundred ceramic discs[seems that many looking anyway ]

tubes are good or new

tube shields are in place and well grounded to chassis

AC plug orientation makes no difference

cap lead dress or positioning makes no difference

grounds are tight solid and good..there are only a few chassis grounds in his thing...components that were originally routed to them are still...

the speaker and associated bracket has been replaced...the ground through there is also 100% solid

the volume control ground is solid...and has not been disturbed at any rate

i finally got around to finishing the install of the new speaker and bracket today,i also redid one of the caps to ground after looking at some "before pics" last week,i noticed i had it all of a inch or so down the rail from where it was originally[yes I'm down to THAT level of desperation!i'll try shit that i know will make no difference!]....i powered it up and the buzz seemed quite nearly gone,the new speaker sounded good!i put the case back on and the buzz is now not only back but louder than ever.....wtf?!??

i have no doubt that this is just a stupid problem,an iffy connection somewhere or at worst one or a few of the multitude of ceramic discs may have failed...or something...but i just give up,the only way i think i'm gonna get any satisfaction out of this thing is to find a very large hammer and smash it to bits...

i christian thee...Bendix...dysfunctional shelf queen...

[Reece]

Let's track down this buzz.
1. Do other radios working off the same wall receptacle buzz? If so, could be something in the house: light dimmer, phone charger, shaver charger, etc. etc. Could even be at the neighbor's.
2. The AC switch is on the volume control, which is hum sensitive. How are the wires to the control routed? They should be tightly twisted to reduce hum and routed away from audio grids.
3. Did you replace the cap from volume control to the grid of the first audio with a new cylindrical cap? Routing of this cap may be critical. Some radios shield this cap. Try this: wrap some foil around the cap careful not to short to the end wires, fasten with tape, and connect foil via test clip to chassis ground: hum may be reduced. If so, devise a permanent connection for same. Sometimes where space permits, placing this cap tight against the chassis has a similar effect, the chassis acting as a shield.

If you could post an underchassis view, maybe two, up close of both sides of chassis, we might spot something.

[quaddriver]

I hate to ressurect old threads, but almsot 5 years later I have found one of these radios, intact, complete, pretty and of course not working.

I have the Rider schematic for the 75P6 and like the OP noticed, it is very different, especially in the area of the power supply.

the OPs pics line up with what I see, there is a 2nd transformer between the filter cap and the output tube that is used as a resistor between the rectifier cap section A and B which then goes to the actual output transformer.

Also missing are the 470ohm resistors (many sets use a 1Kohm resistor to drop the voltage from the first cap section to the voltage used by the rest of the plates, I find a 390ohm 2 watter carbon comp in there. Plus a lot of other differences to darn near make the schematic unusable.

In the intervening 5 years does anyone have a line on the 75P6U model? Beitman does not, Im getting no hits for Sams and Rider just has the non-U version.

Also of curiosity is a 5mfd 50v wax cap with a + end marking where the + is on the B- and the other end is, well elsewhere....it is not in the SCM at all.

90% of the 1/4w resistors in there look like pure-dee-crap so I will swap them out, but I am using a 'replace with what you find' motif rather than 'RTFM' since the SCM is so very wrong.

Id be interested in hearing what you used for a dropping resistor across the Se rectifier. In other sets where I have done this that use the std 22ohm inrush limiter, I settle on a 120-150 ohm resistor given the higher line voltages. (and remove the 22 ohm to boot)

As part of my work I am using a polarized cord and rewiring to the switch to force the rectifier to be hot, that way chassis ground is at or near earth and not -125. Biggest issue I had to get over what I utterly assume is a schematic error where the diode symbol is drawn backwards, try as I might, there was no way I could work it out in my head where that circuit could ever work - if it did it would reverse the polarity across the filter caps.

[Bill Cahill]

Are you sure those quarter watt resistors aren't Half watt??
I almost never see quarter want resistors in tube stuff.
Bill Cahill

[quaddriver]

Originally Posted by Bill Cahill

Are you sure those quarter watt resistors aren't Half watt??
I almost never see quarter want resistors in tube stuff.
Bill Cahill

well thats what I thought, but the parts list Im pretty sure says 1/4, but then again, U models vs non-U. I will likely use 1/2 or larger all over the place.

[quaddriver]

had some time to put into this, I deciphered enough of the power supply to redo it. Have no interest in keeping the stock can around for look, that radio will work, or at least catch fire when I am done

So see the pics below....

First off, I selected a 120ohm 10w resistor behind a 2.5amp, 1000piv diode

I mounted them to a terminal strip (something I REALLY am going to miss getting from radio shack) and then mounted all of this to some spare phenol I keep around.

I mounted all of this on top of the chassis so the diode cannot get hot and the cement resistor can bleed off heat.

That second 'transformer' I pulled the leads back up thru the chassis so they can solder directly. I put a small strip on the bottom, all thru bolted, that bolt and those 2 pins connected to it act as the common point for each cap, which goes to B-, which only touches the actual chassis after it goes thru a 220K resistor.

I used close values, the 40 became 47, the 33 became 33, the 50 became 56 and the 100u-25v I used a 100u-50v (section 4 of the original can)

The leads you see are for the AC input (black) and B+ after the 40u cap, transformer, 30u cap (red wire)

All the other lead lines are being replaced with 20gauge hookup wire (another thing I would get from the shack)

At the same time, I replaced the power cord with a polarized one, and am rewiring such the switch switches the hot side and controls the power supply, filaments and the 'pilot light' which is nothing more than a 7w c9? bulb.

After I initially inspected the radio I did in fact plug it in and it didnt burst into flames and after 20 seconds made the 'my rectifier cap is totally gone' growl.

As I go I am cleaning the chassis with steel wool and everything else. Most wires will be replaced, all wax caps (I count 12) and any small resistor. It does have some ceramic discs that use color codes, I gotta go refresh my memory how to read those, the same values per color as resistors, but the orientation...I think the standard is mmf? shoulda paid more attention in college...

[old_coot88]

Originally Posted by quaddriver

...As I go I am cleaning the chassis with steel wool and everything else.

Oh groannnn (face palm) Please say you didn't....


....use steel wool on the chassis.

[quaddriver]

Originally Posted by old_coot88

Oh groannnn (face palm) Please say you didn't....


....use steel wool on the chassis.

tell me why not? its the light stuff I use on gun barrels - shines it right up. there appears to be no coating on it so it is free to corrode as it sees fit?