Transistorized Stereo 70

[kt88pppamp]

Has anyone you guys known of that build a FET equivalent for a stereo 70 amp? A scenereo such as:

A pair of power FETs replacing the EL-34's.

Small signal fets in place of the 7199 tubes.

A solid state bridge rectfier with a CLC circuit instead of a GZ34.

You probably would not need output transformers as the output impedience would be much lower. The power transformer would be different as you would not need voltage as high. I have seen high voltage fet amps using output transformers.

[EWBrown]

hHere was something closely fitting that description, about 40 years ago, Popular ELectronics published a series of DIY articles about the "Tiger" and "Little Tiger" SS power amps. These used bipolar transistors, and complimentary pair outputs ( MJE 802 and MJE4502 ).

A small company in TX (or was it OK) named South West Technical Products Corporation (or SWTPC) sold PC boards, parts and complete kits. These were decent sounding amps for the late 1960s, but they were very prone to blowing transistors like a string of firecrackers, at the slightest provocation :o Yellow_Light_Colorz_PDT_11

In the late 1970s, I worked at (the now long gone) Digital Equipment Corporation, and some of their large disk drives used a very similar amplifier circuit to drive the "voice coil" head mounts. These drivers, with minor mods, made decent SS power amps, and they even used the same output transistors, albeit with DEC house numbers of DEC802 and DEC4502.

The 21st century version of these amps would lkely be the "chip amps" AKA "gain clones" which can have amazingly good performance for such a simple and inexpensive design. Depending on the actual amp chips used, the power output can be fron 25 to over 70 watts per channel.

/ed B

[burnedfingers]

quote:
but they were very prone to blowing transistors like a string of firecrackers, at the slightest provocation

Not 100% true... Most of the problems associated with the Tigers were due to build quality. I've seen many a Tiger that never had the problems that people associate with them.

I currently still own and use a pair of the Model 210A 250 watt Mono blocks and I have put them up against the popular GAS Ampzilla's and SAE 2400's and they come out the winners. Yes, I have owned many of the SAE models and the GAS Ampzilla line as well as numerous high dollar amplifiers.