Thank you Stefan for another interesting video. Some truly bizarre design choices were made for this unit! Sounds like we haven't seen them all yet. I am very interested to see how it performs once all repairs are completed. Regards, David
In all the amplifiers I've fixed that had blown finals, I'd say about 80% were due to a shorted speaker wire and 20% were due to thermal runaway because the compound had dried up and the amp was pushed hard at a party. This one may also have oscillations. Oh yes, I've seen outputs blow because the speaker used piezo tweeters without any current limit resistor. Those tweeters can measure less than 1 ohm at 30KHz and present a short to the finals if the amp oscillates or has program material fed into it. We can't hear that high, so the operator would never know until a fuse opened....IF it opened. LOL 73 Stefan. Looking forward to PT3 👍
There is no fuse on the secondary side - only the mains fuse. So whatever happens, the finals will be killed - accelerated by a very high bias current. This design is shxx!
Why did they use the same supply for both left and right preamps? I'd would have thought it would be easier to design each channel independently and just replicate them. But I guess this is the magical world of MF....
"Always open to new experiences" You're a wild man, Stefan. Brought a smile to my face. 😊
Thank you Stefan for another interesting video. Some truly bizarre design choices were made for this unit! Sounds like we haven't seen them all yet. I am very interested to see how it performs once all repairs are completed. Regards, David
Me too! Tnx
Best job!!
In all the amplifiers I've fixed that had blown finals, I'd say about 80% were due to a shorted speaker wire and 20% were due to thermal runaway because the compound had dried up and the amp was pushed hard at a party. This one may also have oscillations. Oh yes, I've seen outputs blow because the speaker used piezo tweeters without any current limit resistor. Those tweeters can measure less than 1 ohm at 30KHz and present a short to the finals if the amp oscillates or has program material fed into it. We can't hear that high, so the operator would never know until a fuse opened....IF it opened. LOL 73 Stefan. Looking forward to PT3 👍
There is no fuse on the secondary side - only the mains fuse. So whatever happens, the finals will be killed - accelerated by a very high bias current.
This design is shxx!
Beautiful Goerz multimeters! Or are they BBC or Gossen branded?
You mean the four analog meters? They are Siemens made - in the 70ies and 80ies; type "Multizet"
i'm really curious about the total harmonic distortion of this amplifier. It should be super low or inexistent.
Don´t expect too much
Hello Stefan! Great also on audio frequencyes, not only RF equipment, 73
I1WSM
Tnx! But the basics are alwaxs the same whether AF or RF.
Why did they use the same supply for both left and right preamps? I'd would have thought it would be easier to design each channel independently and just replicate them. But I guess this is the magical world of MF....
For left and right channel is used ONE quad-op-amp which has only one power supply connection for + and - ! So they had to decide....
I'll venture you'll most likely see something even more poorly mechanically designed as the cap placement in this one at some point! ;-)
True, This amp is a nightmare!
🙂👍