UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Amateur and Military Radio

Notices

Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

Reply
 
Thread Tools
Old 3rd Oct 2019, 4:05 pm   #1
Hybrid tellies
Nonode
 
Hybrid tellies's Avatar
 
Join Date: Jan 2004
Location: Bristol, UK
Posts: 2,389
Default Hallicrafters S27

I am taking a look at a Hallicraft S27 receiver. I noticed that the speaker outputs are marked either 500 ohms or 5000 ohms. I service information we have is not totally clear on this but does this mean that the speaker impedance is as high as 500 ohms or 5000 ohms for this receiver?
__________________
Simon
BVWS member
Hybrid tellies is offline   Reply With Quote
Old 3rd Oct 2019, 4:26 pm   #2
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 8,257
Default Re: Hallicraft S27

Quote:
Originally Posted by Hybrid tellies View Post
I am taking a look at a Hallicraft S27 receiver. I noticed that the speaker outputs are marked either 500 ohms or 5000 ohms. I service information we have is not totally clear on this but does this mean that the speaker impedance is as high as 500 ohms or 5000 ohms for this receiver?
It's designed for those load impedances, a bog standard SE output transformer with it's primary connected to the 5k output should do then you can run a 4-8ohm or whatever loudspeaker from its secondary.

Lawrence.

Last edited by ms660; 3rd Oct 2019 at 4:38 pm.
ms660 is offline   Reply With Quote
Old 3rd Oct 2019, 4:26 pm   #3
newlite4
Octode
 
newlite4's Avatar
 
Join Date: Nov 2003
Location: Bath, Somerset, UK.
Posts: 1,432
Default Re: Hallicraft S27

Yes, I am working alongside Simon on this one. It is on loan to the space and radio research group https://www.bath.ac.uk/research-cent...eanic-science/ to determine its parameters. I sourced a 64 ohm speaker temporarily but it needs something better suited. I assumed that the 500 ohm was for speaker and the 5000 ohm was for headphones. As it is on loan, we are unable to modify the set to any extent, it is now over 80 years old, although another staff member is re-capping it. I am a bit off the project now as the teaching labs have started but it is generating a great deal of interest in vintage radio in the department and we plan to purchase a range of these sets for further evaluation.
Neil
__________________
preserving the recent past, for the distant future.
newlite4 is offline   Reply With Quote
Old 3rd Oct 2019, 4:44 pm   #4
usradcoll1
Hexode
 
Join Date: Mar 2017
Location: Cedar Grove, Wisconsin, USA.
Posts: 393
Default Re: Hallicraft S27

Quote:
Originally Posted by ms660 View Post
Quote:
Originally Posted by Hybrid tellies View Post
I am taking a look at a Hallicraft S27 receiver. I noticed that the speaker outputs are marked either 500 ohms or 5000 ohms. I service information we have is not totally clear on this but does this mean that the speaker impedance is as high as 500 ohms or 5000 ohms for this receiver?
It's designed for those load impedances, a bog standard SET output transformer with it's primary connected to the 5k output should do then you can run a 4-8ohm or whatever loudspeaker from its secondary.

Lawrence.
The S-27 is a high-frequency receiver and there isn't too many around!
I have another Hallicrafters receiver that has the same set-up. I did exactly the same as you did!
Later, I acquired the proper speaker and it came equipped with the proper matching transformer.
I have several Hallicrafters receivers in my collection, but not an S-27. It's strictly a high frequency receiver and I didn't desire owning one.
Dave, USradcoll1.
usradcoll1 is offline   Reply With Quote
Old 3rd Oct 2019, 5:16 pm   #5
JohnBG8JMB
Tetrode
 
Join Date: May 2006
Location: Poole, Dorset, UK.
Posts: 71
Default Re: Hallicraft S27

S27 manual can be downloaded foc from bama
http://bama.edebris.com/manuals/hallicra/s27/
Circuit attached -I hope
could not upload files - too big?

Output stage is pushpull 6v6s with 500/5000ohm o/p taPS ON TRANSFORMER.
John
G8JMB
JohnBG8JMB is offline   Reply With Quote
Old 3rd Oct 2019, 5:33 pm   #6
JohnBG8JMB
Tetrode
 
Join Date: May 2006
Location: Poole, Dorset, UK.
Posts: 71
Default Re: Hallicrafters S27

Manual pdf attached
Attached Files
File Type: pdf S27 Service Manual.pdf (860.1 KB, 40 views)
JohnBG8JMB is offline   Reply With Quote
Old 3rd Oct 2019, 7:18 pm   #7
Radio Wrangler
Dekatron
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 12,505
Default Re: Hallicrafters S27

The S27 also played an important role in the discovery of the German navigation-guidance beams for bomber attacks. Look up 'battle of the beams'

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is offline   Reply With Quote
Old 3rd Oct 2019, 7:51 pm   #8
HamishBoxer
Dekatron
 
HamishBoxer's Avatar
 
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 6,898
Default Re: Hallicrafters S27

Got one in the museum here awaiting attention, owned it many years bit like the AR88.

It will be another 2 man lift to get it on the bench or strong woman!
__________________
G8JET BVWS Member and V.M.A.R.S
HamishBoxer is offline   Reply With Quote
Old 3rd Oct 2019, 9:04 pm   #9
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 7,657
Default Re: Hallicrafters S27

Yes, the S27 was designed to feed a 500-Ohm line as standard; that was sort-of commonplace as a way to distribute audio around a site in times-past (just as the "100-Volt" line is used nowadays).

A small transformer can be used to match the 500-Ohm output to a modern low-impedance speaker. It doesn't need to be a perfect impedance-transformation, the S27 has a push-pull output stage so there's plenty of 'oomph' on-tap to override any matching-indiscretions.

[This thread reminds me that I've got a S27 in my to-do pile; it's had the original output-transformer replaced by a modern one to match 8Ohm speakers and the S-meter zero pot moved so the new transformer can fit; since I'll only ever use it on headphones I'm minded to strip-out the bogus transformer, remove the two push-pull output-bottles and wire the headphones direct to the driver stage]
G6Tanuki is offline   Reply With Quote
Old 3rd Oct 2019, 9:09 pm   #10
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 7,657
Default Re: Hallicrafters S27

Quote:
Originally Posted by Radio Wrangler View Post
The S27 also played an important role in the discovery of the German navigation-guidance beams for bomber attacks. Look up 'battle of the beams'

David
Yes, I remember William Woolard talking about this in one of the episodes of "The Secret War" BBC series.

And the S27 [or is it a S36-front-panel on a S27? there was much expediency-based parts-and-assemblies interchange during WWII] was used as part of the instrumentation-test frame for the first nuclear bomb.

https://www.antiqueradios.com/forums...p?f=5&t=272886
G6Tanuki is offline   Reply With Quote
Old 4th Oct 2019, 11:03 am   #11
Hybrid tellies
Nonode
 
Hybrid tellies's Avatar
 
Join Date: Jan 2004
Location: Bristol, UK
Posts: 2,389
Default Re: Hallicrafters S27

Thank you for your helpful comments. I can now clearly understand why they used a 500 ohm line output impedance. Interesting to know that this is what came before the 100v line audio feed systems.
As for the 5000 ohm feed I guess is that most headphones of the day were higher impedance compared to what we have today.
Again many thanks for your help.
__________________
Simon
BVWS member
Hybrid tellies is offline   Reply With Quote
Old 4th Oct 2019, 12:18 pm   #12
Silicon
Octode
 
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 1,020
Default Re: Hallicrafters S27

If I have understood the schematic correctly, headphones plugged into the 'phone jack' are connected to the grid of one of the 6V6 output valves. High impedance headphones only need a few milliwatts to power them. Low impedance headphones were also used by the military.

The switching in the phone jack puts a 4k resistor across the 5k winding of the output transformer.
This puts a load on the output transformer which protects it from 'flashover' damage and impedance mismatch if a speaker is not connected.

Check that the phone jack contacts actually work.

The instruction manual does not give the power rating of the 500 and 5,000 Ohm windings of the output transformer. It suggests that speakers can be connected to both. I would like more proof.

On receivers such as the RCA AR88, some of the output windings are only rated at 10 milliwatts.
Silicon is offline   Reply With Quote
Old 4th Oct 2019, 12:39 pm   #13
ms660
Dekatron
 
ms660's Avatar
 
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 8,257
Default Re: Hallicrafters S27

The output stage is two 6V6's in push pull so the power output will be several watts.

Lawrence.
ms660 is offline   Reply With Quote
Old 4th Oct 2019, 5:51 pm   #14
Silicon
Octode
 
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 1,020
Default Re: Hallicrafters S27

I found a manual for the S-36 receiver which also has a 6V6 push pull output stage.

It has a different arrangement for the headphone output.

In addition to the 500 and 5,000 Ohm grounded windings which are used for an external loudspeaker such as the Hallicrafters PM-23, it has a 600 Ohm balanced to ground winding for headphone and balanced line output.

Both windings are rated at 3 watt. It recommends using a 5 Watt speaker.

The Hallicrafters PM-23 speaker incorporates a 5k Ohm step down transformer for the voice coil.
Silicon is offline   Reply With Quote
Old 4th Oct 2019, 6:54 pm   #15
G6Tanuki
Dekatron
 
G6Tanuki's Avatar
 
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 7,657
Default Re: Hallicrafters S27

The S27 outpuut-transformer also includes a feedback-winding for the tone control.

In the past I recall a trick to avoid replacing the output-transformer in radios with P-P output but only 'high impedance' secondaries on the transformer.

You get a normal single-ended-output-transformer and wire its primary between the two anodes of the P-P stage.

The original P-P transformer then acts, essentially, as a 'centre-tapped choke'. This works well with even a rather small single-ended output-transformer, since it's not having to pass any DC.
G6Tanuki is offline   Reply With Quote
Old 5th Oct 2019, 3:54 am   #16
Argus25
Nonode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,349
Default Re: Hallicrafters S27

One really easy and effective way to get back around the issue with radios with high impedance speaker outputs, is just get a donor transformer with a 1/2 inch square core cross section or a 3/4 square section (something out of an old plug pack/wall wart is fine or some other speakers transformer) and rewind it to be an autotransformer, around 500 turns total and simply put a tap on it to suit your speaker remembering the impedance ratio is the square of the turns ratio. Typically the wire diameter would be in the range of 0.25 to 0.35mm.

This way you get the impedance match correct and you won't have any issues with the frequency response and it will be flat. I did this to match a 32 R speaker to a 100R output on a Zc1 radio
Argus25 is offline   Reply With Quote
Old 7th Oct 2019, 8:34 pm   #17
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 13,574
Default Re: Hallicrafters S27

Quote:
Originally Posted by Hybrid tellies View Post
Thank you for your helpful comments. I can now clearly understand why they used a 500 ohm line output impedance. Interesting to know that this is what came before the 100v line audio feed systems.
As for the 5000 ohm feed I guess is that most headphones of the day were higher impedance compared to what we have today.
Again many thanks for your help.

500ohm is a reasonable match for open wire telephone lines which is probably why it was chosen. 100V line "impedance" depends on how many watts are available from the source amplifier..


Old style headphones were typically 2000 ohm which isn't too bad a match for a 5000 ohm output, though with p-p 6V6s, you'd need to watch the volume control!
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is offline   Reply With Quote
Old 8th Oct 2019, 5:26 pm   #18
WB6NVH-GEOFF
Triode
 
Join Date: Aug 2013
Location: Monterey, California USA
Posts: 32
Default Re: Hallicrafters S27

The 500 and 5000 Ohm outputs are both speaker outputs, not headphone and not line outputs. Yes, 500 Ohms was a common line output impedance but there is also something called "line level" which this is not. This is speaker level audio.

In the early 1930's, 5000 Ohms was a common speaker line impedance, probably with magnetic speakers, hence this impedance being found here.

The way you use this today is with a matching transformer to 4-8 Ohms and a modern speaker. I usually use a 70 Volt public address "ceiling speaker" transformer with the correct tap selected, as they are cheap and easy to find. In a pinch a 6 volt filament transformer run "backwards" connected to the 500 Ohm output will also work.
WB6NVH-GEOFF is offline   Reply With Quote
Old 8th Oct 2019, 10:24 pm   #19
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 13,574
Default Re: Hallicrafters S27

Surely the filament transformer would need to be connected forwards as a normal stepdown? 5W or so at 500R is around 50V.


Over here with a 240V primary, it would be a fair match to a 4 ohm speaker fed from the 5000 ohm output.
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 2:12 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2019, Paul Stenning.