Output Transformer questions / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Output Transformer questions

previous 1 2 3 4 next last

Move Thread

LAN_403

Proud Mary

Sun Dec 08 2013, 01:30PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Sigurthr wrote ...

Ahh, thank you for the info, PM!

Sig, you absolutely can't go wrong if you follow the Mullard 'showcase' designs, which include everything from circuit diagrams, complete lists and specifications of parts, engineering drawings of chassis and front panel metal work with chassis punch and drill sizes required, PCB layouts for those that like them, with alternative classical point-to-point tagboard layouts, with the position of every R and C on the tagboards shown.

The Mullard Three Watt Economcal Stereophonic Amplifier is here:

The Mullard Ten Watt High Quality Stereophonic Amplifier circuit and constructional details is here:

The Mullard 5-20 Twenty Watt Amplifier is here:

These amplifiers were designed by the AF valves division of Mullard to show their valves performing at their very best, so if you follow their designs closely you can be certain of having a really good amplifier at the end of it.

Ash Small

Sun Dec 08 2013, 03:57PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I'd just like to add that unless you have a matched pair of output transformers and speakers, it's not worth considering a stereo amp.

I'm taking a different approach, in that I'm using what's available, and modifying Chris's 'Mighty Atom' circuit to suit. I won't consider building a stereo one until I have a suitable pair of output tranny's, etc.

Shrad

Sun Dec 08 2013, 04:55PM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

you also have to get matched tubes if you go push-pull, or find a design where each and every tube has its own bias circuit

in that way of thinking, I guess you could set up a compensation network to adjust a transformeter response and match the response

Mads Barnkob

Sun Dec 08 2013, 05:11PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

You do not have to use matched output tubes, even if you get matched tubes, after some hundred hours they are no longer matched.

This is why you have adjustable bias balance and build in some meters to monitor the anode current through measuring voltage drop over the cathode resistor.

If you are thinking about building a PP EL34 amplifier, the Mullard 5-20 is standard, but consider reading Claus Byrith excellent paper on modifying it to modern times and make up for some of its shortcomings.

Proud Mary

Sun Dec 08 2013, 08:45PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Transformerless audio valve output with high impedance speakers.

In the late 1950s Philips produced 400Î© and 800Î© speakers in a brave attempt to abolish the problems of the output transformer in push pull circuits for good.

They also produced a 700Î© speaker which formed the anode load of a UCL82 (ECL82 with a high voltage heater) for use in budget radios such as Philips B2G25U, Cossor CR1202U and the Stella ST113U. The valve's anode current, about 40mA, flowed through the speaker winding. UCL82 has a rated load impedance of 5.6kÎ© at 200V, which is a very long way from the 700Î© speaker's ~800Î© AC impedance, but it still sounds better than the equivalent model radios which used a transformer.

Ash Small

Sun Dec 08 2013, 09:18PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Proud Mary wrote ...

Transformerless audio valve output with high impedance speakers.

In the late 1950s Philips produced 400Î© and 800Î© speakers in a brave attempt to abolish the problems of the output transformer in push pull circuits for good.

They also produced a 700Î© speaker which formed the anode load of a UCL82 (ECL82 with a high voltage heater) for use in budget radios such as Philips B2G25U, Cossor CR1202U and the Stella ST113U. The valve's anode current, about 40mA, flowed through the speaker winding. UCL82 has a rated load impedance of 5.6kÎ© at 200V, which is a very long way from the 700Î© speaker's ~800Î© AC impedance, but it still sounds better than the equivalent model radios which used a transformer.

So we should just forget about output Xformers, and 'wind our own' speakers, instead?

Proud Mary

Sun Dec 08 2013, 10:35PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Ash Small wrote ...

So we should just forget about output Xformers, and 'wind our own' speakers, instead?

Well it's a thought! a lot of very fine wire...

Conundrum

Mon Dec 09 2013, 06:22AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

I found some nice "half C" cores in the flat screen inverters I dismantled.

Just a though Ash.

EDIT: A source of fine copper wire is dead analogue clocks from charity shops, for some reason they still can't seem to check them for leaking batteries.

-A

johnf

Mon Dec 09 2013, 08:46AM

Registered Member #230 Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284

Why try to go to low impedance speakers. I have built electrostatic speakers with 0.25 (mil) mylar rubbed by hand with grahite to make the diapham and perforated plates for the two outer electrodes.
Plates to the outer electrodes and the diaphram earthed is one way or connect the pushpull output to the diaphram and earth the outer perforated plates

sounds incredible bass could do with a sub woofer as mine were only 2 foot by 4 foot for the diaphrams

this appeared in the audio amateur magazine in the late seventies
all credits go to Saunders who put up the original article.

Shrad

Mon Dec 09 2013, 08:53AM

Registered Member #3215 Joined: Sun Sept 19 2010, 08:42PM
Location:
Posts: 780

what is the quality of the sound you'd have?

if they are not as good as commercial low impedance speakers, I can't see the point of not using a crappy transformer with some crappy tubes

I'll have to try out the dirty one... I gathered parts for a dual PP 6080 with power toroids as output transformers, and I guess it would be as good as anything I'd be able to put out together out of tubes, as I have no experience about common best practices with tubes

as soon as I'm ready I'll make this amp

previous 1 2 3 4 next last

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob