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[Steve M Smith]

In the UK in the mid to late 1970s, HH was the king of the pub band PA world.

A couple of weeks ago a friend asked me to have a look at two of his amplifiers which he bought around 1976.

One is a five channel mixer amplifier and the other is a slave amplifier.  Both are rated at 100 watts and have two 2N3055 transistors in the output stage. Quite a basic design.  HH together with Carlsbro had the majority of the market at that time but by the early 1980s we had been invaded by Peavey and pub bands started buying their superior designs such as the XR500 and XR600.



They didn't need a lot to get working again.  There were a couple of loose crimp terminals on a bridge rectifier and a few wires which needed re-soldering... and a lot of contact cleaner sprayed into the pots.

Behind the front panels of these amplifiers, there is an electroluminescent panel - so when the power is on, all of the panel lettering glows bright green.  The one on the mixer amp doesn't work any more but the slave one sort of works.  It's a bit patchy.

is what they looked like when new:
 

[Guy Graham]

Beautiful, thanks for posting that!

The backlit front panel is something I haven't seen for maybe 20 years. It really brought back some warm memories of gigging as a youngster.

I noticed HH are making a limited range of equipment again. However nothing on their current site is pretty in the same way as classics like the IC100 unfortunately.

[Ivan Beaver]

Both are rated at 100 watts and have two 2N3055 transistors in the output stage. Quite a basic design. .[/img]

100 watts out of 2 3055s is really pushing it.  4 yes-but 2?

But I guess it depends on "how you measure the watts"----------

There were a lot of products back then that liked to use "peak watts", "instantaneous peak" etc to appear louder than they actually were.

Of course the power supply voltage would be the BIG KEY to how much power it "could" possibly produce.  At least in terms of voltage swing.

[Steve M Smith]

100 watts out of 2 3055s is really pushing it.

Looking at this circuit: http://s652.photobucket.com/user/kvimbo/media/temp/HH_S130.jpg.html?t=126736549 it would appear to be a pair of 2N3773s.  I was sure they were 2N3055s.

Anyway, next up on the repair bench is an old Marshall JTM45.  One of the early ones with a hand bent aluminium chassis.


Steve.

[Bob Leonard]

100 watts out of 2 3055s is really pushing it.  4 yes-but 2?

But I guess it depends on "how you measure the watts"----------

There were a lot of products back then that liked to use "peak watts", "instantaneous peak" etc to appear louder than they actually were.

Of course the power supply voltage would be the BIG KEY to how much power it "could" possibly produce.  At least in terms of voltage swing.

The 3055 is one of those three legged dummies that is practically indestructible, but I agree 100 watts is pushing hard. Might work if the heat sink was a Maytag freezer.

[Peter Morris]

The 3055 is one of those three legged dummies that is practically indestructible, but I agree 100 watts is pushing hard. Might work if the heat sink was a Maytag freezer.

The HH amp should have 2N3773's in it - the voltage rating of the 2N3055 is not high enough to give an acceptable SOA

http://www.onsemi.com/pub_link/Collateral/2N3773-D.PDF
http://www.onsemi.com/pub_link/Collateral/2N3773-D.PDF


oops sorry Steve missed your post.

[John Roberts {JR}]

Yup, the 3055s were hard to kill but slower than dirt***... The 2N3773 was a faster part so a better choice for audio amps, but a single pair will still be heat sink limited for output power (150W per device would require being heat sunk to an ice berg). My personal DIY amp I built back in the early '70s used several 2N3773s in parallel to make 250W @8 ohm (a lot of power for back then).

You will recognize the all too common quasi-complementary output stage, probably lifted from some manufacturer's application note. The PNP power devices of the day were not up to the task so a small PNP in front of another power NPN handled the PNP side of the signal swing.

JR

 *** ironically perhaps, the original (slow) 2n3055 have become collectors items for audio-phools trying to replicate the exact sound of old legacy products that used them as line driver buffers and the like. Device manufacturers probably couldn't make one that slow now if they tried, and they aren't trying. The 2n3055 was so ubiquitous in designs that several versions of them came out trying to hold on to all those design-ins.

[Ivan Beaver]

 *** ironically perhaps, the original (slow) 2n3055 have become collectors items for audio-phools trying to replicate the exact sound of old legacy products that used them as line driver buffers and the like. Device manufacturers probably couldn't make one that slow now if they tried, and they aren't trying. The 2n3055 was so ubiquitous in designs that several versions of them came out trying to hold on to all those design-ins.

And when they listen to the different amps they can hear a difference-so somewhere in their minds that makes it "better" SIMPLY because it is different-NOT better or more accurate-but "different".

And that is all that matters to some people-------------  They like the fact that they can hear a difference

[Steve M Smith]

There is nothing on those amplifiers which you could call a heatsink.  Just the metal case.  I wouldn't want to run them at 100 watts for too long!


Steve.

[John Roberts {JR}]

And when they listen to the different amps they can hear a difference-so somewhere in their minds that makes it "better" SIMPLY because it is different-NOT better or more accurate-but "different".

And that is all that matters to some people-------------  They like the fact that they can hear a difference

An unfortunate reality when selling expensive snake oil is it helps to sound different, when you are arguing how much better you are.

Modern gear that generally sounds more alike than different tends to favor value manufacturing.

JR 

[Ivan Beaver]

There is nothing on those amplifiers which you could call a heatsink.  Just the metal case.  I wouldn't want to run them at 100 watts for too long!


Steve.

This was real common back then. 

[Steve M Smith]

It was quite a revelation in the 1980s to see the large heatsinks on the Peavey XR series compared with the minimal attempts to get rid of heat employed by HH and Carlsbro.


Steve.

[duane massey]

There was a local company during the early, early 70's that mounted the power transistors on pieces of wood with holes for ventilation. Now THAT was a heatsink.....

[John Roberts {JR}]

There is nothing on those amplifiers which you could call a heatsink.  Just the metal case.  I wouldn't want to run them at 100 watts for too long!


Steve.

For <100W a moderate sized metal chassis/case "could" supply sufficient surface area to dissipate heat from. If the chassis is made from the typical steel, that will provide lower heat transfer so not work as well as a full aluminum chassis (an aluminum heat spreader could help some). The familiar finned aluminum heat sink gets the extra surface area from all the fins, and in top of the fins, if you look closely there are small grooves in the surface of the fins, this grooved surface increases the total surface area even more. 

While large enough chassis could dissipate much of a small amplifier's heat, using a compact "real" heat sink allows you to design a standard power module that could be used in multiple SKUs, instead of every product requiring a different new heat sink design.

JR

[Steve M Smith]

I think the chassis is steel.  The transistors are mounted on the back behind a cover plate.




Steve.

[Mike Diack]

 *** ironically perhaps, the original (slow) 2n3055 have become collectors items for audio-phools trying to replicate the exact sound of old legacy products that used them as line driver buffers and the like. Device manufacturers probably couldn't make one that slow now if they tried, and they aren't trying. The 2n3055 was so ubiquitous in designs that several versions of them came out trying to hold on to all those design-ins.

Does this mean my big box of OC35s (Ft=220kHz) is going to be worth something some day ?.
I live in hope :-)
M

[John Roberts {JR}]

Does this mean my big box of OC35s (Ft=220kHz) is going to be worth something some day ?.
I live in hope :-)
M

Not to me... 

The driving force for popularity of original 3055 devices is apparently some old Neve recording products that used them back in the day. I don't even recognize OC35s, 3055 were used everywhere, in everything (long time ago).. 

JR

[Steve M Smith]

OC35 was a germanium power transistor in a TO3 package.


Steve.

[John Roberts {JR}]

OC35 was a germanium power transistor in a TO3 package.


Steve.

These may have some use in special effects, like fuzz tone guitar pedals.

JR

[Steve M Smith]

These may have some use in special effects, like fuzz tone guitar pedals.

The OC71 was the low power version.  Scrape off the paint and you turn it into an  OCP71 phototransistor! (I think I remember that correctly).


Steve.

[Mike Diack]

The OC71 was the low power version.  Scrape off the paint and you turn it into an  OCP71 phototransistor! (I think I remember that correctly).


Steve.

Until those rotters at Mullard caught on and started filling them with opague thermal goo instead of the transparent stuff. I guess they were annnoyed at loosing out on the extra five bob they could charge for the OCP version. I suspect JR doesn't recognise these because they wear bowler hats and drink tea.
M

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