Many many years ago (early or mid 1970s) I bought an HH power amp. The amp was a bare chassis with two power amps fed from a common power supply. The amps were I was told used to power monitors in broadcasting ( I assumed the BBC but that was never actually stated) with one side of the amp used for bass and the other for treble ie one chassis for each monitor speaker.
What was odd on these amps is that the output stages were power Darlington's with HH numbers (I never found out what they really were) which ran amazingly cool - especially when you consider the output of the amps was rated at 60W each into 8 ohms and 100w each into 4 ohms. There were no real heat-sinks on the devices - only a "u" shaped chassis of stout gague aluminium onto which the output devices and other components were mounted.
The amps in my opinion were first class in terms of quality (but that was a very long time ago) but did have one terrible weakness - there was not real protection for the output devices which if presented with a very low impedance load or overdriven would simply run away and cook the circuit boards - this happened twice to me, one when I accidentally presented a 2 ohm load to the amps and on another occasion when a speaker lead came loose and shorted in one of the speaker plugs. Despite that it got repaired and carried on working for many years but eventually I sold it in the late 1980s.
I have always wondered about these amps and often scanned Ebay in the hope of finding an undamaged one for sale somewhere. Does anyone else have any experience of them or their history - which was probably pretty short? I did know of one company in the midlands which used them a lot, Midland Sound Services run by a guy called Ken Dibble but he stopped trading yonks ago - he also used a vast beast of a valve amp which was based on a rebuilt Vortexion 200w - but that's another story.
What was odd on these amps is that the output stages were power Darlington's with HH numbers (I never found out what they really were) which ran amazingly cool - especially when you consider the output of the amps was rated at 60W each into 8 ohms and 100w each into 4 ohms. There were no real heat-sinks on the devices - only a "u" shaped chassis of stout gague aluminium onto which the output devices and other components were mounted.
The amps in my opinion were first class in terms of quality (but that was a very long time ago) but did have one terrible weakness - there was not real protection for the output devices which if presented with a very low impedance load or overdriven would simply run away and cook the circuit boards - this happened twice to me, one when I accidentally presented a 2 ohm load to the amps and on another occasion when a speaker lead came loose and shorted in one of the speaker plugs. Despite that it got repaired and carried on working for many years but eventually I sold it in the late 1980s.
I have always wondered about these amps and often scanned Ebay in the hope of finding an undamaged one for sale somewhere. Does anyone else have any experience of them or their history - which was probably pretty short? I did know of one company in the midlands which used them a lot, Midland Sound Services run by a guy called Ken Dibble but he stopped trading yonks ago - he also used a vast beast of a valve amp which was based on a rebuilt Vortexion 200w - but that's another story.
