• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). There are daily reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Vintage amplifiers that could challenge or approach current state of the art amplifiers

Holmz

Major Contributor
Joined
Oct 3, 2021
Messages
1,283
Likes
759
Location
Australia
Which 4 Ohm speakers?

Take your pick, many modern speakers are 4 ohm impedance.



What is an 8 Ohm amp?.

Take your pick, the thread is vintage, and only a few of the vintage amps would reliably drive a low impedance load.



So by your way of reasoning, an amp rated to deliver 80, 100, 150W into 8 Ohms would be "sketchy" delivering 50W into a 4 Ohm load? Alright.

^yeah exactly^
My reasoning is that any amp, which looses its magic smoke when pushing a 4 ohm load, is not a 4 ohm “capable” amp.

If the amp does not say “4 ohm” somewhere on the box, label or in the manual, then I would be a bit hesitant to hook it up to a 4 ohm or 2 ohm load.

But I am not overly brave, so YMMV.
 
OP
restorer-john

restorer-john

Master Contributor
Joined
Mar 1, 2018
Messages
9,608
Likes
27,331
Location
Gold Coast, Queensland, Australia
My reasoning is that any amp, which looses its magic smoke when pushing a 4 ohm load, is not a 4 ohm “capable” amp.

I don't know of a single vintage amplifier that has failed due to a 4R load. All amplifiers tested back in the day by most major review magazines, tested them into 'half the manufacturer's rated impedance' which was either 4R or 2R.

I've just been restoring several mid 1970s amplifiers/receivers and they can run into 4R at full power all day.
 

GXAlan

Major Contributor
Forum Donor
Joined
Jan 15, 2020
Messages
1,172
Likes
1,900
I don't know of a single vintage amplifier that has failed due to a 4R load. All amplifiers tested back in the day by most major review magazines, tested them into 'half the manufacturer's rated impedance' which was either 4R or 2R.

I've just been restoring several mid 1970s amplifiers/receivers and they can run into 4R at full power all day.

I sent in the JBL SA600 for that very reason. It handles 4 ohms just fine and only blew fuses because the FTC rule didn’t exist and the advertisements doubled the wattage for two channels.

Edit: it is more likely the late 80s and early 90s budget stuff that will fail
 

Gorgonzola

Addicted to Fun and Learning
Joined
Jan 27, 2021
Messages
678
Likes
890
Location
Southern Ontario
Does anyone have an opinion and/or measurements for the notorious Phase Linear 400?

I guess it was most infamous as the "Flame Linear" because of its tendency to blow up when driven hard.

I owned one for 20 years and It was my primary amp for all that time. I eventually came to understand that the thing sounded terrible -- treble in particular was at once glassy harsh and opaque. At one point I had the power supply capacitors replace with new, higher value ones; it still sounded like poop. My first replacement amp for it was a NAD C 270 which was a considerable improvement.

qzhovyq3jxoc.jpg
 

Pattern

Member
Joined
Dec 6, 2021
Messages
38
Likes
48
Is the Adcom GFA-555 too young?
 

Doodski

Grand Contributor
Forum Donor
Joined
Dec 9, 2019
Messages
13,682
Likes
13,476
Location
Canada
Does anyone have an opinion and/or measurements for the notorious Phase Linear 400?

I guess it was most infamous as the "Flame Linear" because of its tendency to blow up when driven hard.

I owned one for 20 years and It was my primary amp for all that time.
Some of them auto loosen the screws that fasten the output transistors down to the heatsink. A good fix is to change out the screws for longer screws and add-on lock nuts so they can't come loose.
 
OP
restorer-john

restorer-john

Master Contributor
Joined
Mar 1, 2018
Messages
9,608
Likes
27,331
Location
Gold Coast, Queensland, Australia
Can someone confirm the original Phase Linear output transistors were actually high voltage, electronic ignition transistors (maybe for an early CDI or injector duty?) repurposed for use in the amplifier? That's always been my belief. The part numbers were also Delco part numbers- GM's electronic division.

If that is true, there is some irony here and some significance.

The MOSFETs used in Bruno Putzey's ground breaking Class D designs are also automotive injector driver devices, repurposed for his amplifiers.
 

Doodski

Grand Contributor
Forum Donor
Joined
Dec 9, 2019
Messages
13,682
Likes
13,476
Location
Canada
The MOSFETs used in Bruno Putzey's ground breaking Class D designs are also automotive injector driver devices, repurposed for his amplifiers.
What are they. I spec'd a IRFZ44 to 175C. I wonder what the ones you speak of do. IRFZ44 was veryyy common in high end car amps.
 

G|force

Active Member
Forum Donor
Joined
Apr 8, 2021
Messages
210
Likes
227
Location
Gualala, CA
Take your pick, many modern speakers are 4 ohm impedance.




Take your pick, the thread is vintage, and only a few of the vintage amps would reliably drive a low impedance load.




^yeah exactly^
My reasoning is that any amp, which looses its magic smoke when pushing a 4 ohm load, is not a 4 ohm “capable” amp.

If the amp does not say “4 ohm” somewhere on the box, label or in the manual, then I would be a bit hesitant to hook it up to a 4 ohm or 2 ohm load.

But I am not overly brave, so YMMV.
Point taken @Holmz. I should have elaborated that one '4 Ohm' 6 inch 2-way with a simple passive crossover, a cap and a choke and maybe a couple resistors, is not necessarily the same as another '4 Ohm' multi-driver array that manages to be seen as a '4 Ohm speaker' with series parallel shenanigans. (Polk SDA-SRS)
I am very familiar with the odor or Eau de Ohmite and while the smoke is heart breaking, It can smell rather sweet if not burning too much before sound stops.
*Phenols*
I love the magic smoke but rather keep it inside.

I'm not beefing on the real and true visual art that some vintage amplifiers have.
I love to look at them.
Some are beautiful and I share in the nostalgia, I love to look at your photos, everyone.
 

Plcamp

Addicted to Fun and Learning
Joined
Jul 6, 2020
Messages
656
Likes
802
Location
Ottawa
Awesome amplifier. I'd put it up in the classic list for sure.
The 555, 545 and 535 look very similar schematically, and I think the latter two use same PCB, with the 545 populating an extra set of output transistors on a bigger heatsink.

Edit: I saw a note in a stereo review from 1985 that said the 555, with a mod, can handle load down to 1 ohm. Not sure what the mod is.

Edit2: Just because I think this is cool…Here is a site where a gent used the transformers from a 2535 unit, plus the 535II boards with an extra pair of output transistors to produce a very high current 90W/ ch unit. Nice work IMO.

 
Last edited:

Sal1950

Grand Contributor
The Chicago Crusher
Forum Donor
Joined
Mar 1, 2016
Messages
10,944
Likes
11,857
Location
Central Fl
The 555, 545 and 535 look very similar schematically, and I think the latter two use same PCB, with the 545 populating an extra set of output transistors on a bigger heatsink.
535 & 545 Series 1, A bit different but very similar.. ;)
wpid-20150831_131354.jpg


Adcom%20GFA%20545,,,.jpg
 

DonH56

Master Contributor
Technical Expert
Forum Donor
Joined
Mar 15, 2016
Messages
6,567
Likes
12,681
Location
Monument, CO
Can someone confirm the original Phase Linear output transistors were actually high voltage, electronic ignition transistors (maybe for an early CDI or injector duty?) repurposed for use in the amplifier? That's always been my belief. The part numbers were also Delco part numbers- GM's electronic division.

If that is true, there is some irony here and some significance.

The MOSFETs used in Bruno Putzey's ground breaking Class D designs are also automotive injector driver devices, repurposed for his amplifiers.
I certainly do not remember off-hand, but after some searching I found this: https://web.archive.org/web/20080706175948/http://www.hometown.aol.com/phasetek/faqoutput.html

That matches my vague memory of buying a bunch of Delco transistors to keep on hand as spares.

HTH - Don
 

Holmz

Major Contributor
Joined
Oct 3, 2021
Messages
1,283
Likes
759
Location
Australia
Can someone confirm the original Phase Linear output transistors were actually high voltage, electronic ignition transistors (maybe for an early CDI or injector duty?) repurposed for use in the amplifier? That's always been my belief. The part numbers were also Delco part numbers- GM's electronic division.

If that is true, there is some irony here and some significance.

The MOSFETs used in Bruno Putzey's ground breaking Class D designs are also automotive injector driver devices, repurposed for his amplifiers.

It puts the spark in the music.
 
OP
restorer-john

restorer-john

Master Contributor
Joined
Mar 1, 2018
Messages
9,608
Likes
27,331
Location
Gold Coast, Queensland, Australia

DonH56

Master Contributor
Technical Expert
Forum Donor
Joined
Mar 15, 2016
Messages
6,567
Likes
12,681
Location
Monument, CO
Interesting Don, thanks for digging in the back shed of your brain for me. So they were only a 3.5A Ic rated transistor, massively paralleled. High voltage, lowish current, lowish selected gain and massively stacked. I think I prefer the modern way...
Indeed, me too! :D
 
OP
restorer-john

restorer-john

Master Contributor
Joined
Mar 1, 2018
Messages
9,608
Likes
27,331
Location
Gold Coast, Queensland, Australia
They are an excellent preamplifier with little to criticise about the design. What I love about them is the complete left/right separate power supplies right back to the transformer and very careful layout.

The ALPs bowden cable linked switches can get noisy/intermittent in their old age and it is a big job to properly fix. (I'll post up a link to yesterday's rainy day Rotel project).

Enjoy. :)
 
Top Bottom