The 90s, Angela Instruments - Classic Audio

Servicing, restoring and listening to classic audio gear 

Test Bench late '92-early '93

I was living in my aunt's basement and repaired classic audio equipment for Angela Instruments there.

JE's classic tube preamp picks

Marantz 7C

Looks and build quality aside, the following three preamps sound better to my ears than the Marantz 7C.

Pilot SP215 - full function with cool VU meters. Big, dark and octal-like sound. The tape head input on this preamp is superb. SP216 is essentially the same but more deluxe faceplate and knobs.

Eico ST84 - limited only by its cheap looks, but very well designed circuit. This sounds fast and detailed without harshness.

Another Stewart Hegeman wide bandwidth design is the Lafayette KT600, but unlike the Citation I, this used only 12AX7s, no 12AT7s to make it sound dark and bland. This is full range and dynamic!

JE's PP EL34 Ultra Linear amps picks

The evergreen Marantz 8B

The SA260 is Pilot's best effort in building a PP EL34 amp. Better than a stock Dyna ST70 but not quite in the same league as the Eicos below or the 8B above. Very sweet and three dimensional midrange, but not quite as fast in the bottom and top end.

This Eico HF87 was my first restoration project for Angela Instruments. Elegant circuit - 1/2 a 12AX7 direct coupled to a long-tailed pair of 6SN7s driving cathode biased EL34s. The HF89 is very similar except the EL34s were run fixed bias. I prefer the HF87!

Eico HF60 monoblocks - similar to the above except this now uses a pentode EF86 direct coupled to a long tail phase inverter 6SN7 driving EL34s in fixed bias. Tube rectified using a 5AR4. The heart and soul of this amp is the Acro TO330 output transformer. To my ears, this is an even better amp than the Marantz 8B. The only tweak I did to this amp was install a choke in the power supply in lieu of a resistor.  

JE's collection of PP EL84 Ultra Linear amps

Dyna ST35

This particular unit was so rusty I decided to repaint it. Very simple circuit, the 7247 is essentially a twin triode wherein the first section is like a 12Ax7 direct coupled to a 12AU7 cathodyne phase inverter. To take advantage of its wide bandwidth ability, I removed the input coupling cap. I used this a lot to drive the BBC LS3/5As and Quad ESLs.

Pilot SA232 - just like its big brother, beautiful midrange but compared to the other three, this sounds a bit soft at the frequency extremes. Tube rectified power supply.

Leak 20 - Mullard style circuit using 3 x 12AX7. A 12AU7 would have worked better in the long tail phase inverter position, but then the amp would not have enough sensitivity for the matching Troughline preamp which essentially has no line stage and just a 2 stage EF86 phono preamp. Tube rectified power supply using a GZ34 just like the SA232. I kept mine in stock form and used a voltage divider to lessen the input sensitivity.

Acrosound 20/20 - the Loftin-White PP amp, no caps in the signal path. If you get lucky enough to own one, make sure all the resistors have not drifted, otherwise the performance deteriorates. This is a design wherein the bandwidth is limited only by the output transformer.

I unloaded all these EL84 amps to finance Tango and Tamura OPT acquisitions.  I should really have kept the *ST35* for posterity because it was the first tube amp I bought and spent the longest listening hours with it.