Forums :: Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives :: Books
Support This Site: Contributors :: Advertise


It is currently Nov Thu 22, 2018 12:03 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 10 posts ] 
Author Message
 Post subject: Radio build question!
PostPosted: Dec Sat 09, 2017 1:11 am 
Member
User avatar

Joined: Mar Fri 17, 2017 4:44 pm
Posts: 37
Location: Peekskill, NY
Hey guys, I'm building a small 2 tube radio featured in a Popular Science publication. I was wondering about the volume control switch, which is labeled right after the B+ circuit. Does only one line of the power cord go to the volume switch and then only one connection goes out of the switch to that capacitor, or is that resistor on the end of that capacitor a variable resistor making that the volume pot, in that case what kind of switch should I use and what should I connect to that volume pot? I'm pretty sure that is a variable resistor but I'm just making sure, I wanted to have a volume pot and on off switch but idk if that'll be possible, I'll just stick to the schematics then if you cant directly do that

Image

Also on a side note does anybody know where I can get Zenith Y723 knobs? I haven't seen any reproductions and can't find any lose ones for sale online, starting to consider buying another Y723 just for the knobs but I really don't want to separate another radio from its original knobs and replace them with improper ones


Top
 Profile  
 
 Post subject: Re: Radio build question!
PostPosted: Dec Sat 09, 2017 1:18 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 12932
Location: S. Dartmouth MA 02748-1225 USA
Use a separate switch for the AC power. The so-called volume control is a control for regeneration and locating a 25k linear pot with a switch is a difficult item.

You are aware that this is a hot chassis receiver and there is a power line shock danger :shock:

Use a "safety" cap for the .0005 volume control (regeneration) coupling cap as it is common to the AC line, its failure if shorted could be shocking...

It appears the set was to use a resistance line cord. Be careful of the wattage and location of the 220 ohm filament dropping resistor, it may get hot... Resistor line cords are not available. Also, seems the set was intended to use a high impedance speaker. These are unobtainable in a 40's era style. Alternative is an output transformer and a PM speaker. A salvage from a retired AA5 radio should work well...

IMHO I think this circuit is a knock off of a two tube economy radio built in the WWII era...

GL

Chas

_________________
First they ignore you, then they laugh at you, then they fight you, then you win.
"Gandhi"


Last edited by Chas on Dec Sat 09, 2017 1:27 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Radio build question!
PostPosted: Dec Sat 09, 2017 1:24 am 
Member
User avatar

Joined: Mar Fri 17, 2017 4:44 pm
Posts: 37
Location: Peekskill, NY
Also, what should I do about the No.30 D.S.C wire for the tickler, I can't seem to find some online or in NOS, does the diameter need to be exact or is the oscillation needed not really that sensitive as long as I have 35 turns in it


Top
 Profile  
 
 Post subject: Re: Radio build question!
PostPosted: Dec Sat 09, 2017 1:30 am 
Member
User avatar

Joined: Mar Fri 17, 2017 4:44 pm
Posts: 37
Location: Peekskill, NY
Chas wrote:
Use a separate switch for the AC power. The so-called volume control is a control for regeneration and locating a 25k linear pot with a switch is a difficult item.

You are aware that this is a hot chassis receiver and there is a power line shock danger :shock:

Use a "safety" cap for the .0005 volume control (regeneration) coupling cap as it is common to the AC line, its failure if shorted could be shocking...

It appears the set was to use a resistance line cord. Be careful of the wattage and location of the 220 ohm filament dropping resistor, it may get hot... Resistor line cords are not available. Also, seems the set was intended to use a high impedance speaker. These are unobtainable in a 40's era style. Alternative is an output transformer and a PM speaker. A salvage from a retired AA5 radio should work well...

IMHO I think this circuit is a knock off of a two tube economy radio built in the WWII era...

GL

Chas



What wattage would you recommend I use then?


Top
 Profile  
 
 Post subject: Re: Radio build question!
PostPosted: Dec Sat 09, 2017 1:47 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 12932
Location: S. Dartmouth MA 02748-1225 USA
WAG for the 220 use a 10 watt power resistor and mount in an open space, not next to wood!

As a school project IE touchy-feely, this is a very dangerous undertaking, despite changes. You may do far better with some sort of battery tube design or solid state circuit. The 32 volt tube will run HOT as will the filament dropping resistor.

With solid state at 6-9 volts fingers can be all over it and all that will happen is it will either go into oscillation or stop working...

With a battery tube design an uncomfortable shock could occur but there is no risk of serious shock or burn...

_________________
First they ignore you, then they laugh at you, then they fight you, then you win.
"Gandhi"


Last edited by Chas on Dec Sat 09, 2017 1:51 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Radio build question!
PostPosted: Dec Sat 09, 2017 1:50 am 
Member
User avatar

Joined: Mar Fri 17, 2017 4:44 pm
Posts: 37
Location: Peekskill, NY
I was thinking of that but there's no real fun in that, I think working with non solid state designs are more fun and more of a challenge and more rewarding, I've built solid state radios before- rather try and do this


I'll keep in mind a battery tube radio. But wouldn't I need like a 45 volt battery, which really aren't made anymore?


Top
 Profile  
 
 Post subject: Re: Radio build question!
PostPosted: Dec Sat 09, 2017 2:07 am 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 12932
Location: S. Dartmouth MA 02748-1225 USA
DragCat352 wrote:
I was thinking of that but there's no real fun in that, I think working with non solid state designs are more fun and more of a challenge and more rewarding, I've built solid state radios before- rather try and do this
I'll keep in mind a battery tube radio. But wouldn't I need like a 45 volt battery, which really aren't made anymore?


For common battery tubes from late 40's, 50's the plate current is very small and 5 9-volt transistor radio batteries snapped together will work for many hours. A "D" battery used to power 1 volt filaments will also give some 6-8 hours. "D" batteries in parallel will work proportionately longer.

Common Dollar Store batteries are fine.

There are a LOT of good, safe, battery tube circuits out there, some very similar to the line powered design, in fact it may be practical to convert this design. However, forward success could get shaky...

I DO understand the initial project and I support you. However, bringing the line power radio into a classroom where there may be other students that do not understand the risks is not a good idea.

See what others have to say. <<<<

If you don't find the wire drop me another PM, I'll check in the Attic and see if I have some 30 ga.

BTW what is the size of the coil form? Diameter and length.

I have a derelict Ham radio project battery radio that uses small plug in forms and does short wave. I may have a circuit drawing or know where it was designed from, I think an old QST article...

Chas

_________________
First they ignore you, then they laugh at you, then they fight you, then you win.
"Gandhi"


Top
 Profile  
 
 Post subject: Re: Radio build question!
PostPosted: Dec Sat 09, 2017 5:30 am 
Member

Joined: Nov Tue 14, 2017 5:09 am
Posts: 840
Location: Austin, Texas
Take a look at this regen radio: http://www.bobsdata.com/regenerative_receiver/
It's much safer with 45V battery power. You could use 5x9V batteries in series to get that voltage.
Also the 1T4 and 3V4 tubes will be much easier to find and will be low priced if you have to buy them.
Wire size isn't all that critical for the coils. Something in the 20 to 32 AWG range should work OK.
You do need to keep the space between the coils the same as with the original wire size.

For hand wound coils, double sided tape like used to put things in a scrapbook can help a lot.
Put the tape around the coil form in the area of the winding to hold each turn in place.
To prevent damage, coat the windings with clear fingernail polish after you get everything working.


Top
 Profile  
 
 Post subject: Re: Radio build question!
PostPosted: Dec Sat 09, 2017 11:53 am 
Member

Joined: Dec Sun 14, 2008 3:33 pm
Posts: 739
Location: Tokyo
I would use more readily available tubes. For example, a 6SK7 instead of the 7A7. Maybe a 6G6 instead of the 32L7. You could even use two 6G6 tubes.

Or, if 7-pin miniature tubes are acceptable: a 6BA6 for the 7A7, a 6AK6 for the 32L7. Again, this could be built using two 6AK6 tubes. There are many choices if you don't mind using miniatures. Almost anything could be made to work. What do you have on hand?

As suggested, use a set of 9V batteries in series for the B+. The current drawn is so low, they'll last 6 months to a year. For the heaters, use a small 6 volt transformer.

The battery tubes (1L4, 3V4, etc) work fine. However, if you're looking for vacuum tube 'glow', you won't get it with them.

You'll need an audio output transformer, not shown in the schematic. Also, with just one audio stage, you can't expect much volume. This is really a headphone receiver.

Rob


Top
 Profile  
 
 Post subject: Re: Radio build question!
PostPosted: Dec Sat 09, 2017 4:27 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 26895
Location: Detroit, MI USA
The actual dissipation in the 220Ω filament dropping resistor is a whopping 19.8 watts. Given the standard practice of at least doubling the rating, you would need to use no less than a 40 watt resistor (not common) there and would be best served with a 50 watter, which is going to get quite hot and need to be bolted to a substantial heat sink.

I agree with the others, there are safer ways to do this, but if you insist on an AC powered set using tubes go with 6 volt ones, put the filaments in parallel and use a small power transformer with a 6 volt secondary to run them from.

The way this is designed, it needs to be operated from an isolation transformer to be safer for someone to use. It should also be in a completely enclosed non-metallic case, with insulated knobs on the tuning and regeneration controls.

Back in those days, lots of totally unsafe circuit designs were published in magazines because people had sense enough to use them properly but today that is impossible and someone could easily get killed by touching certain parts of this circuit while power is applied. The frame of the variable capacitor, among many other components, is directly connected to one side of the AC line!

A far better choice would be a set using battery filament tubes as others have mentioned. There are plenty of circuits around for 2 tube sets that don't use AC power and don't have the potential of killing someone.

_________________
Dennis

Experience is what you gain when the results aren't what you were expecting.


Top
 Profile  
 
Post New Topic Post Reply  [ 10 posts ] 

All times are UTC [ DST ]


Who is online

Users browsing this forum: Exabot [Bot] and 4 guests



Search for:
Jump to:  
























Privacy Policy :: Powered by phpBB