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


It is currently Dec Mon 18, 2017 1:52 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 118 posts ]  Go to page Previous  1, 2, 3, 4, 5, 6  Next
Author Message
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Tue 11, 2017 6:59 pm 
Moderator

Joined: Jul Tue 18, 2006 5:23 am
Posts: 10932
Location: Roseville,Ca
What kinda meter are you using??Always start with the highest range until you know what voltage you should see,you can always range down to get a more precise reading.

Do you have a dim-bulb tester built yet?

Have you powered up the radio to 110 volts yet?

It probably isn't gonna do much at 84 volts-min would be 105 or so before it will work.
Phil

_________________
I've been doing so much for so long with so little I can now do anything with nothing!


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Tue 11, 2017 7:07 pm 
Member
User avatar

Joined: Jan Thu 26, 2017 10:33 pm
Posts: 370
I have a dim bulb tester, but I was using a variac. I have a radioshack dmm that can take up to 600v. I just thought that the 75 voltage was getting pretty high, and since it wasn't going down when I left it at 84 volts, I thought it would only get higher as I went up. I had the radio on 115v or so when I tested the 42 tube. Thanks for the information! I'll test again at a whole 115v.

_________________
No matter how smart you are, there is always someone smarter than you.

-Unknown


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Tue 11, 2017 7:12 pm 
Member
User avatar

Joined: Jan Thu 26, 2017 10:33 pm
Posts: 370
Okay. Got all the way to 115v and the plate voltage for the 75 measured 200v! The radio was operating with slightly louder volume than usual, but was still relatively quiet.

_________________
No matter how smart you are, there is always someone smarter than you.

-Unknown


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Tue 11, 2017 9:55 pm 
Member
User avatar

Joined: Jan Thu 26, 2017 10:33 pm
Posts: 370
What could be the cause of this? Is this the reason for the set's low volume? The capacitors and resistors connected to the plate of the 75 are all new and in spec. Should I continue making voltage measurements? Am I asking too many questions?

_________________
No matter how smart you are, there is always someone smarter than you.

-Unknown


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Tue 11, 2017 11:02 pm 
Moderator

Joined: Jul Tue 18, 2006 5:23 am
Posts: 10932
Location: Roseville,Ca
When you say it's "operating" is it receiving stations?Do you have an antenna/long wire hooked to the ANT terminal?
Nice loud hum when touching the top cap of the 75 with your finger?
Yes,measure voltages and list them like the chart does then compare-see any big differences?
Phil

_________________
I've been doing so much for so long with so little I can now do anything with nothing!


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Tue 11, 2017 11:23 pm 
Member
User avatar

Joined: Jan Thu 26, 2017 10:33 pm
Posts: 370
It receives several stations without an antenna, and it receives more with one. I have been touching the top of the 75 tube with a screwdriver and getting a noticeable hum. It might be louder if I touch it with my finger. Also, I will continue to make measurements on the tube voltages.

_________________
No matter how smart you are, there is always someone smarter than you.

-Unknown


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Wed 12, 2017 4:35 am 
Moderator

Joined: Jul Tue 18, 2006 5:23 am
Posts: 10932
Location: Roseville,Ca
I gotta ask-if it works why are you still "fixing" it?? :lol:
Phil

_________________
I've been doing so much for so long with so little I can now do anything with nothing!


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Thu 13, 2017 12:45 am 
Member
User avatar

Joined: Jan Thu 26, 2017 10:33 pm
Posts: 370
LOL, Didn't realize that I said it was working. Working to me means operating enough to pick up a few audible stations. Restored or repaired to me means fixed 100%.

_________________
No matter how smart you are, there is always someone smarter than you.

-Unknown


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Thu 13, 2017 3:31 am 
Moderator

Joined: Jul Tue 18, 2006 5:23 am
Posts: 10932
Location: Roseville,Ca
You did say it is receiving,has the volume improved now?
Phil

_________________
I've been doing so much for so long with so little I can now do anything with nothing!


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Thu 13, 2017 3:02 pm 
Member
User avatar

Joined: Jan Thu 26, 2017 10:33 pm
Posts: 370
Yes, it is receiving, but no, the volume has not improved. I haven't been doing much testing on it, and have been spending most of my time working on the cabinet, which was a total wreck. I'll try to get some voltage measurements today.

_________________
No matter how smart you are, there is always someone smarter than you.

-Unknown


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Fri 21, 2017 10:37 pm 
Member
User avatar

Joined: Jan Thu 26, 2017 10:33 pm
Posts: 370
Okay, here are (most of) the voltages. I couldn't measure anything on the 6a7 because it was positioned right above the bandswitch, making it impossible to get a good connection with the tube pins. When I have a long period of time, I might try to measure it. Anyways, here are the voltages I recorded minus the 80 rect. tube. (a --- means there was no voltage listed for the tube):

Recorded Voltages

Tube/Plate v/Filament v/Screen v/Cathode v
75 /190v /7.15v /---------/1.94v
42 /281v /7.10v /283v /19v
6d6 /290v /7.14v /124v /6.8v(6d6 tube next to 42 tube)
6d6 /267v /6.92v /125v /6.6v(6d6 tube next to electrolytics)

Voltages Listed Schematic

Tube/Plate v/Filament v/Screen v/Cathode v
75 /95v /6v /---------/1.25v
42 /230v /6v /240v /18v
6d6 /230v /6v /95v /5.8v(6d6 tube next to 42 tube)
6d6 /240v /6v /95v /5.8v(6d6 tube next to electrolytics)

Do these voltages seem to be OK compared to the listed voltages in the schematic?

_________________
No matter how smart you are, there is always someone smarter than you.

-Unknown


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Sat 22, 2017 3:27 am 
Member
User avatar

Joined: Jan Thu 26, 2017 10:33 pm
Posts: 370
The volume control measures 5k ohms across its two side terminals and 5k ohms from its middle terminal to chassis (ground). It is still connected, and when I tried to attach a 500k ohm resistor across it, it stayed at 5k ohms. Is this because it is connected into the circuit? I remember buying a 500k ohm volume pot, unless I misread the label.

_________________
No matter how smart you are, there is always someone smarter than you.

-Unknown


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Sat 22, 2017 12:44 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 7751
Location: Cleona, PA
There's your problem. You have a 5K (5000 ohm) volume control installed. It is shorting much of the signal to ground. The schematic calls for a 0.5 meg (500K, or 500,000 ohm) volume control. Get one with audio taper.

_________________
Reece


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Sat 22, 2017 2:03 pm 
Member
User avatar

Joined: Jan Thu 26, 2017 10:33 pm
Posts: 370
I tried to sub a 500k ohm resistor across the two taps (both sides), but the resistance stayed at 5k ohms. Is this normal? I might be able to pick up a 500k volume control today.

_________________
No matter how smart you are, there is always someone smarter than you.

-Unknown


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Sat 22, 2017 2:05 pm 
Member
User avatar

Joined: Jan Thu 26, 2017 10:33 pm
Posts: 370
If I can't get one today, does this look good? http://www.ebay.com/itm/RADIOSPARES-500 ... Sw44BYNIs3

Also, do I have to disconnect the wires on the potentiometer to get a correct reading? Do I have to remove all of the tubes to measure the resistance on the pot accurately?


EDIT:

The pot in that link doesn't work. It has no switch.

_________________
No matter how smart you are, there is always someone smarter than you.

-Unknown


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Sat 22, 2017 2:07 pm 
Moderator

Joined: Jan Thu 01, 1970 1:00 am
Posts: 36085
Location: Livermore, CA
You need to remove the 5,000 ohm control first. Adding resistance across another resistor can only make the value lower.

_________________
Norm


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Sat 22, 2017 2:28 pm 
Member
User avatar

Joined: Jan Thu 26, 2017 10:33 pm
Posts: 370
Duh! I feel stupid. Values only add when resistors are in series. I just remembered that. Does it matter that my volume control is hooked up when I take the measurements?

_________________
No matter how smart you are, there is always someone smarter than you.

-Unknown


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Sat 22, 2017 8:02 pm 
Member
User avatar

Joined: Jan Thu 26, 2017 10:33 pm
Posts: 370
Okay, I think this one should work:

http://www.ebay.com/itm/PC375-500Kohm-A ... Sw4A5YwH4T

_________________
No matter how smart you are, there is always someone smarter than you.

-Unknown


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Sat 22, 2017 8:34 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 7751
Location: Cleona, PA
Hi, I sent you a Private Message.

_________________
Reece


Top
 Profile  
 
 Post subject: Re: American Bosch Model 450 Low Volume Issue
PostPosted: Jul Mon 31, 2017 2:06 am 
Member
User avatar

Joined: Jan Thu 26, 2017 10:33 pm
Posts: 370
I disconnected the original volume control, and it read 500k, so that's not the problem. Any ideas what is? One of the 6d6s is marginal in emissions testing.

_________________
No matter how smart you are, there is always someone smarter than you.

-Unknown


Top
 Profile  
 
Post New Topic Post Reply  [ 118 posts ]  Moderators: Marcc, Norm Leal Go to page Previous  1, 2, 3, 4, 5, 6  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: Eickerman, John Bartley, johnnyreece, Tube Radio and 18 guests



Search for:
Jump to:  


















Privacy Policy :: Powered by phpBB