The Texan Amplifier - UK Vintage Radio Repair and Restoration Discussion Forum

DigitalNoMore · 30th Nov 2020, 12:56 pm

Split from this thread

https://www.vintage-radio.net/forum/...d.php?t=173687

Cheers

Mike T

I remember building a Texan from a kit back in the 70s.
It used power darlingtons for the output transistors and 741 op-amps in the preamp.

The sound quality was noticeably better after upgrading the op-amps I seem to remember.

Pity it ended up at the local tip years ago!

Jerry

Ted Kendall · 30th Nov 2020, 3:05 pm

TIP31/41 aren't Darlingtons, although the output stage, unusually, has voltage gain. The designer stretched to 748s in two slots, if memory serves. Remembered fondly!

Boulevardier · 30th Nov 2020, 3:34 pm

Quote:

Originally Posted by DigitalNoMore

Pity it ended up at the local tip years ago!

Jerry

Story of our lives, really!

Mike

Kala_12 · 30th Nov 2020, 4:14 pm

I remember building one of those back in the day. I remember the sound was bit 'weedy' even when driving 12" speakers with midax horns.
One of the channels died (it didn't take any of the speakers with it). I never did get it working again and like Jerry's, mine ended up at the tip.
For anyone interested, it was PW May 1972 (onwards). https://worldradiohistory.com/UK/Pra...PW-1972-05.pdf
Stuart.

Keith956 · 30th Nov 2020, 4:18 pm

I built one from a kit in the 1970's. Worked OK until I sold it to a friend and within a week the output transistors blew. I replaced them FOC but then after a few months they blew again! Surprisingly we still remained friends

DigitalNoMore · 1st Dec 2020, 5:28 pm

Seems my memory let me down!

It was a PE Orion I had which used BD699, BD700 power darlingtons in the output stage.

Jerry

Radio Wrangler · 1st Dec 2020, 6:09 pm

Mr Mann worked for Texas Instruments, so the Texan was a bit of a showcase for their transistors and opamps.

The article came out while I was doing my BSc, and lots of people bought kits. On top of all the bad joints and parts in the wrong places, there was the issue of students winding them up full and trying to run them for hours at parties. I wound up fixing an awful lot of them, and I've been left feeling they're a bit fragile.

David

Ian - G4JQT · 1st Dec 2020, 7:00 pm

Thank you! That really brings back memories of me assembling that on the floor of the Bursars House in RG4 8TZ! Happy days...

I think my brother acquired it eventually and God knows what happened to it after that.

stevehertz · 1st Dec 2020, 7:19 pm

I upgraded mine with the later toroidal transformer (much better bass) and 1456 ICs to replace the industrial 741s. I had the original Henry's Radio cardboard box in which the transformer was shipped to me until a few months ago.

There was a virtual production line of the metal cabinet work going on in the metal shop at Thorn as 90% of the components were available 'free' from the company. Only today I dug out my much modified Texan to look for a particular switch.

Trevor · 1st Dec 2020, 7:31 pm

Yes they were a classic used sensibly quite nice not a disco amp agreed
I used to repair quite a few back in the day
A design exercise rather than a design classic but on reflection no worse than a lot of budget offerings of its time
Trev

ajs37 · 2nd Dec 2020, 12:06 pm

Having built one in the '70s (can't remember what happened to it), I've now got one on my todo list - only problem has been sourcing replacements for 741s (not that I've tried too hard yet!!). If I remember correctly the output Trannies are suspect as well!
Cheers
Andy

Ted Kendall · 2nd Dec 2020, 4:15 pm

Mann's original assessment of the adequacy of the heatsinking was that the prototype ran barely warm in the lab on "a moderately deafening output of Simon and Garfunkel". A frend built one and blew it a couple of times, eventually beefing it up with TIP41/42s and better heatsinks, in which form it ran well for some time. Never had any problems with mine, once Dad had sorted out my goofs - perhaps I was lucky, or my speakers were more efficient..

stevehertz · 2nd Dec 2020, 4:33 pm

Quote:

Originally Posted by ajs37

Having built one in the '70s (can't remember what happened to it), I've now got one on my todo list - only problem has been sourcing replacements for 741s (not that I've tried too hard yet!!). If I remember correctly the output Trannies are suspect as well!
Cheers
Andy

Unless you're determined to go original, there are much better drop in replacements for 741s that are audio friendly.

MeerKat · 5th Dec 2020, 12:29 am

I built one from a kit back in the day as well, at first switch on a couple of the op amps ran hot and the output was mono, I found the outputs of two opposite channel op amps shorted due to to a copper track bridge, a sharp knife sorted that.

My brother killed a set of output transistors by too much volume, a heatsink was fitted to stop that happening again. It used to suffer from switching thumps whenever any switch in the house was operated, the mod that came out to stop that worked well.

I still have it, I would like to get a set of pots for it, the originals are getting scratchy now.

Trevor · 5th Dec 2020, 1:02 pm

Yes I found that any amp fitted with 741,s was prone to switching noise
The texan was an early inroad for a lot of DIY enthusiast's
It felt modern and showed many an amatuer the way forward re electronics
Trev

MrBungle · 5th Dec 2020, 1:04 pm

Yep. Built a few audio filters with 741's. They're ok if you like your music in a room full of hissing snakes

.

Definitely better opamps out there to use...

Radio Wrangler · 5th Dec 2020, 2:24 pm

The 741 is quite noisy.

The 741 is also running out of gain before the top end of the audible spectrum and consequently feedback is having reduced effect at controlling distortion and determining input and output impedances.

They were used in all sorts of things back in the day. They were OK in low gain stages with big enough signal voltages, so you'll come across tales of them in mixing desks not being too bad.

The primary design intent was as a sales promotion for Texas Instrument's semiconductors, and it served its purpose well.

There are plenty of newer devices that will yield improvements which ought to be audible. Even the contemporary LM301A with the advantage of its external compensation can out-perform the 741 in this sort of application.

David

Ted Kendall · 5th Dec 2020, 2:43 pm

The 741 has its place in history largely through being the first op-amp which was reasonably robust and stable. True, the compensation was of the "bind, gag and set in treacle" variety, but compared to the 709 which preceded it, the thing was a least of some use. The 748 needed external compensation which could of course be tailored to the applcation, as it was in the Texan.

Trevor · 6th Dec 2020, 11:25 am

I can remember paying about £5 for a 741 from RS back in the day really new tech back then ! I did a few experiments with it before it was damaged never thought they would catch on!
As for the 709 a nice sounding op amp much better than the 741
Dual amplifiers used the 709 and they sounded nice
Trev

30th Nov 2020, 12:56 pm	#1
DigitalNoMore Pentode Join Date: Jan 2013 Location: Nottingham, Notts. UK. Posts: 228	The Texan Amplifier Split from this thread https://www.vintage-radio.net/forum/...d.php?t=173687 Cheers Mike T I remember building a Texan from a kit back in the 70s. It used power darlingtons for the output transistors and 741 op-amps in the preamp. The sound quality was noticeably better after upgrading the op-amps I seem to remember. Pity it ended up at the local tip years ago! Jerry

30th Nov 2020, 3:05 pm	#2
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,675	Re: Texan amplifier. TIP31/41 aren't Darlingtons, although the output stage, unusually, has voltage gain. The designer stretched to 748s in two slots, if memory serves. Remembered fondly!

30th Nov 2020, 4:14 pm	#4
Kala_12 Hexode Join Date: Dec 2012 Location: Carmarthen, Carmarthenshire, UK. Posts: 268	Re: Texan amplifier. I remember building one of those back in the day. I remember the sound was bit 'weedy' even when driving 12" speakers with midax horns. One of the channels died (it didn't take any of the speakers with it). I never did get it working again and like Jerry's, mine ended up at the tip. For anyone interested, it was PW May 1972 (onwards). https://worldradiohistory.com/UK/Pra...PW-1972-05.pdf Stuart. __________________ Half my stuff is junk - luckily, my wife doesn't know which half!

30th Nov 2020, 4:18 pm	#5
Keith956 Heptode Join Date: Jun 2019 Location: Oxfordshire Posts: 740	Re: Texan amplifier. I built one from a kit in the 1970's. Worked OK until I sold it to a friend and within a week the output transistors blew. I replaced them FOC but then after a few months they blew again! Surprisingly we still remained friends

1st Dec 2020, 5:28 pm	#6
DigitalNoMore Pentode Join Date: Jan 2013 Location: Nottingham, Notts. UK. Posts: 228	Re: Texan amplifier. Seems my memory let me down! It was a PE Orion I had which used BD699, BD700 power darlingtons in the output stage. Jerry

1st Dec 2020, 6:09 pm	#7
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,902	Re: Texan amplifier. Mr Mann worked for Texas Instruments, so the Texan was a bit of a showcase for their transistors and opamps. The article came out while I was doing my BSc, and lots of people bought kits. On top of all the bad joints and parts in the wrong places, there was the issue of students winding them up full and trying to run them for hours at parties. I wound up fixing an awful lot of them, and I've been left feeling they're a bit fragile. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

1st Dec 2020, 7:00 pm	#8
Ian - G4JQT Octode Join Date: Jun 2004 Location: Reading/Fakenham, UK. Posts: 1,326	Re: Texan amplifier. Thank you! That really brings back memories of me assembling that on the floor of the Bursars House in RG4 8TZ! Happy days... I think my brother acquired it eventually and God knows what happened to it after that.

1st Dec 2020, 7:19 pm	#9
stevehertz Dekatron Join Date: Sep 2011 Location: Rugeley, Staffordshire, UK. Posts: 8,835	Re: Texan amplifier. I upgraded mine with the later toroidal transformer (much better bass) and 1456 ICs to replace the industrial 741s. I had the original Henry's Radio cardboard box in which the transformer was shipped to me until a few months ago. There was a virtual production line of the metal cabinet work going on in the metal shop at Thorn as 90% of the components were available 'free' from the company. Only today I dug out my much modified Texan to look for a particular switch. __________________ A digital radio is the latest thing, but a vintage wireless is forever..

1st Dec 2020, 7:31 pm	#10
Trevor Octode Join Date: Aug 2006 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 1,082	Re: Texan amplifier. Yes they were a classic used sensibly quite nice not a disco amp agreed I used to repair quite a few back in the day A design exercise rather than a design classic but on reflection no worse than a lot of budget offerings of its time Trev

2nd Dec 2020, 12:06 pm	#11
ajs37 Heptode Join Date: Jun 2003 Location: Bristol, UK. Posts: 900	Re: Texan amplifier. Having built one in the '70s (can't remember what happened to it), I've now got one on my todo list - only problem has been sourcing replacements for 741s (not that I've tried too hard yet!!). If I remember correctly the output Trannies are suspect as well! Cheers Andy

2nd Dec 2020, 4:15 pm	#12
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,675	Re: Texan amplifier. Mann's original assessment of the adequacy of the heatsinking was that the prototype ran barely warm in the lab on "a moderately deafening output of Simon and Garfunkel". A frend built one and blew it a couple of times, eventually beefing it up with TIP41/42s and better heatsinks, in which form it ran well for some time. Never had any problems with mine, once Dad had sorted out my goofs - perhaps I was lucky, or my speakers were more efficient..

5th Dec 2020, 12:29 am	#14
MeerKat Hexode Join Date: Jan 2016 Location: Ramsgate, Kent, UK. Posts: 298	Re: The Texan Amplifier I built one from a kit back in the day as well, at first switch on a couple of the op amps ran hot and the output was mono, I found the outputs of two opposite channel op amps shorted due to to a copper track bridge, a sharp knife sorted that. My brother killed a set of output transistors by too much volume, a heatsink was fitted to stop that happening again. It used to suffer from switching thumps whenever any switch in the house was operated, the mod that came out to stop that worked well. I still have it, I would like to get a set of pots for it, the originals are getting scratchy now. __________________ Andrew Illegitimi non carborundum Last edited by MeerKat; 5th Dec 2020 at 12:30 am. Reason: Clarity

5th Dec 2020, 1:02 pm	#15
Trevor Octode Join Date: Aug 2006 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 1,082	Re: The Texan Amplifier Yes I found that any amp fitted with 741,s was prone to switching noise The texan was an early inroad for a lot of DIY enthusiast's It felt modern and showed many an amatuer the way forward re electronics Trev

5th Dec 2020, 1:04 pm	#16
MrBungle Dekatron Join Date: Jun 2016 Location: London, UK. Posts: 3,687	Re: The Texan Amplifier Yep. Built a few audio filters with 741's. They're ok if you like your music in a room full of hissing snakes . Definitely better opamps out there to use...

5th Dec 2020, 2:24 pm	#17
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,902	Re: The Texan Amplifier The 741 is quite noisy. The 741 is also running out of gain before the top end of the audible spectrum and consequently feedback is having reduced effect at controlling distortion and determining input and output impedances. They were used in all sorts of things back in the day. They were OK in low gain stages with big enough signal voltages, so you'll come across tales of them in mixing desks not being too bad. The primary design intent was as a sales promotion for Texas Instrument's semiconductors, and it served its purpose well. There are plenty of newer devices that will yield improvements which ought to be audible. Even the contemporary LM301A with the advantage of its external compensation can out-perform the 741 in this sort of application. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

5th Dec 2020, 2:43 pm	#18
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,675	Re: The Texan Amplifier The 741 has its place in history largely through being the first op-amp which was reasonably robust and stable. True, the compensation was of the "bind, gag and set in treacle" variety, but compared to the 709 which preceded it, the thing was a least of some use. The 748 needed external compensation which could of course be tailored to the applcation, as it was in the Texan.

6th Dec 2020, 11:25 am	#19
Trevor Octode Join Date: Aug 2006 Location: Stoke-on-Trent, Staffordshire, UK. Posts: 1,082	Re: The Texan Amplifier I can remember paying about £5 for a 741 from RS back in the day really new tech back then ! I did a few experiments with it before it was damaged never thought they would catch on! As for the 709 a nice sounding op amp much better than the 741 Dual amplifiers used the 709 and they sounded nice Trev