Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Instruments and Amps Everything that makes music, Especially including instrument amps.

Repurpose of old radio
Repurpose of old radio
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 30th January 2019, 04:35 PM   #1
Rasped is offline Rasped  Denmark
diyAudio Member
 
Join Date: Mar 2006
Location: Aarhus
Default Repurpose of old radio

Hi

I have a pretty old radio.
A Bang & Olufsen Grand Prix 43K.
But it is a mess, wires are cracking, capacitors melting or leaking, the works.

I can't find the schematics to do a proper rebuild, and I don't really need a long wave radio anyway.

So what I want to do is build a guitar amp out of the parts.

My problem is, I can't for the life of me figure out how to use the UBL1 power tubes. They are dual diode, single pentode.
And i can't figure out if any of the other tubes can be used as a preamp.

So, I am looking for someone to design a circuit using the UBL1 tubes, and maybe some of the others if needed. It doesn't have to be fancy, with a tone stack etc. Just simple.
I just need the amplifier circuit, I should be able to do the power supply by myself.

I'm willing to pay up front for the service.

/R
  Reply With Quote
Old 30th January 2019, 06:29 PM   #2
Printer2 is offline Printer2  Canada
diyAudio Member
 
Join Date: Apr 2010
I would not bother with the tubes from the radio. I could not find the exact radio but usually a manufacturer does not try to reinvent the wheel when making many products. This one shows the same output tube. The UBL21 is the replacement tube. https://www.vintageshifi.com/reperto...-Schematic.pdf

Quote:
So I've got a question: The filament of UBL1 is 55V@0.1A, and the plate + screen voltages are low, under 200V.
I'm thinking about using one 230V:115V power transformer for everything: First, getting the B+ of about 145V with a bridge (although it seems a bit low) and then putting a VR90 tube (I've got one nice ST) and wiring the heater of UBL1 in series with some preamp tubes to get 90V total. There are several choises for 0.1A heaters tubes, but the cheap tubes are mostly noval or 7-pin type which looks not good together with UBL1. There's a UF9 pentode that looks proper, but it's a bit expensive ($13.90 at Antique Electronics) and the heater is 12.6V so I will need three of them. I may wire them as triodes and it'll be fine but still a bit too Xpensive.

Is there a problem with this setup - first B+, then 0.1A heaters from the same secondary?

And if that's okay, what other tubes may fit the preamp
Got oddball tubes!
https://frank.pocnet.net/sheets/046/u/UBL1.pdf

Now the problem you have is you do not have a power transformer and the radio is directly off the line, not good for something you are attached to through your strings. The best I could suggest is get another output tube that can use the 3.5k ohm output transformer. Measure the speaker impedance to get the ratio if you use other than the stock speaker. Then use a 'standard' tube type rather than use the tube set in the radio. Not what you probably want to hear but more practical.
  Reply With Quote
Old 30th January 2019, 06:36 PM   #3
Parafeed813 is offline Parafeed813  Netherlands
diyAudio Member
 
Join Date: Aug 2012
One question first: does the radio have a power transformer?
U- tubes (100mA series heater) were often operated directly from the mains.
The UBL1 has a 55V heater. Before you continu make sure you have a power transformer with that voltage, or the combined voltage of the series of U-type tubes.
  Reply With Quote
Old 30th January 2019, 06:41 PM   #4
Rasped is offline Rasped  Denmark
diyAudio Member
 
Join Date: Mar 2006
Location: Aarhus
The name of the radio up above is a link to the model.

There is a power transformer in the radio. It's running on 240v here in europe, and there's a huge plug on the back of the radio i can use if I need to change the input voltage. Very versatile system I must say.

I'll snap some photos and upload, so hang on.

Last edited by Rasped; 30th January 2019 at 06:46 PM.
  Reply With Quote
Old 30th January 2019, 06:50 PM   #5
Rasped is offline Rasped  Denmark
diyAudio Member
 
Join Date: Mar 2006
Location: Aarhus
Oh, and that schematic might be useful. But I have 2 tubes, and I haven't built a push pull amp before... so... more reading I guess.
  Reply With Quote
Old 30th January 2019, 06:51 PM   #6
stephen_keller is offline stephen_keller  United States
diyAudio Member
 
Join Date: Dec 2004
Location: Portland, OR
Quote:
Originally Posted by Rasped View Post
Hi

I have a pretty old radio.
A Bang & Olufsen Grand Prix 43K....

So what I want to do is build a guitar amp out of the parts.

My problem is, I can't for the life of me figure out how to use the UBL1 power tubes. They are dual diode, single pentode.
And i can't figure out if any of the other tubes can be used as a preamp.

/R
The 43K has two UBL1 tubes presumably used for its power amplifier. It is probable that these are already configured as a push-pull power amp in a reasonable manner. In other words, you might be able to use the output stage as is. Trace out the schematic and see what it's doing. You may have to strap the anodes of the diodes to ground or the cathodes if they aren't already.

You can use one of the UCH4 (heptode/triode) tubes as a phase inverter. Refer to page 159 in this data sheet: http://www.mif.pg.gda.pl/homepages/f...046/u/UCH4.pdf.

The UF9 will serve well as an audio preamp or intermediate gain stage.

The extra UCH4 can be employed as a gain stage with some creative thinking or abandoned.

I'd ditch the UY1 rectifier, install (a presumably missing power transformer) and use a more common full-wave rectifier.

If you want to keep the UM4 as a VU meter of sorts, that'd be interersting or you could ignore it.

The main challenge to this sort of conversion is that the tube complement for this radio is intended for a series heater arrangement across a 220 volt a.c. supply (probably with a dropping resistor). Using these will require some thought to get the heaters working reasonably.

Stph
  Reply With Quote
Old 30th January 2019, 06:58 PM   #7
Rasped is offline Rasped  Denmark
diyAudio Member
 
Join Date: Mar 2006
Location: Aarhus
I've attached some pictures. One is showing the powertubes... and what is that thing next to it? it was covered in an aluminium tube. One is showing the big plug on the back side that controls what input voltage it accepts. One is showing the rectifier tube, just because. And one is showing the input transformer.

Don't know which order they are in. Very archaic messageboard I must say

Quote:
Originally Posted by stephen_keller View Post
The 43K has two UBL1 tubes presumably used for its power amplifier. <snip>
I have downloaded LTspice and will try to draw out the circuit. I just realised I have A LOT to learn still. Thank you so much for your help so far, I'll probably have more questions soon.

This is quite a step up from a 12AX7 + EL84 amp.
Attached Images
File Type: jpg IMG_20190130_204410.jpg (415.7 KB, 208 views)
File Type: jpg IMG_20190130_204222.jpg (465.6 KB, 207 views)
File Type: jpg IMG_20190130_204236.jpg (364.0 KB, 209 views)
File Type: jpg IMG_20190130_204333.jpg (303.4 KB, 203 views)
  Reply With Quote
Old 30th January 2019, 08:53 PM   #8
Printer2 is offline Printer2  Canada
diyAudio Member
 
Join Date: Apr 2010
Oops, thought it was single ended. https://www.vintageshifi.com/reperto...ice-Manual.pdf

And using the superseding replacement tube of the UBL1. https://www.vintageshifi.com/reperto...-Schematic.pdf
  Reply With Quote
Old 31st January 2019, 12:49 AM   #9
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: Maine USA
Quote:
Originally Posted by Rasped View Post
There is a power transformer in the radio....
This is NOT a safe candidate for a guitar amp.

It is "Hot Chassis". The audio common is connected to the power line without transformer *isolation*.

Yes, it has a huge choice of line voltages. It does this with series/parallel combinations of heaters and a small autotransformer (not isolating) for the higher AC lines.

Note in particular: it has options for DC power lines. You can't change DC voltage with a transformer, but the B+ can be fed straight DC, from 110V to 150V, with an added resistor or at reduced maximum output. (DC power lines were somewhat common in industrial districts into the 1950s.)

Hot chassis is safe *for radio*. Radio waves in, sound waves out, the user never touches the circuit. But a guitar player holds one side of the circuit in his hands while touching grounded objects.

Last edited by PRR; 31st January 2019 at 12:51 AM.
  Reply With Quote
Old 31st January 2019, 10:55 AM   #10
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Quote:
Originally Posted by Rasped
There is a power transformer in the radio.
The link says it is an AC/DC set, so it has no power transformer. This is to be expected for a set using 100mA heater valves. It is therefore not safe for use for audio, unless completely rebuilt in the power supply area. Much easier to start from scratch or with a kit.
  Reply With Quote

Reply


Repurpose of old radioHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Repurpose Old Bakelite Valve Radio Unit Ohkie Construction Tips 9 1st July 2016 01:54 PM
Repurpose vertical output autoformer? Wigwam Jones Tubes / Valves 16 1st October 2015 03:40 AM
Repurpose an X-BoSoZ PSU still4given Power Supplies 3 15th April 2014 01:42 PM
Which industrial transformer to repurpose? ozerik Power Supplies 3 28th December 2010 12:34 PM
repurpose wall wart a good idea? gary h Power Supplies 8 11th January 2010 06:55 PM


New To Site? Need Help?

All times are GMT. The time now is 02:27 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki