Eico HF-60's power supply. - diyAudio
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Old 24th November 2013, 11:51 PM   #1
Zekk is offline Zekk  Singapore
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Default Eico HF-60's power supply.

Hi Folks!

I'm seeking advice for the power supply for my stereo bloc built based on David C. Gillespie's mod for Eico's HF-60.

A GZ34 > 20uf > 3H > 20uf > 1K3 > 20uf > 51K > 20uf was configured for a monobloc.

My question is, does it have enough amperage to power a stereo bloc?

Wish to build it like those Western Electric or Altec style..... vintage look!
So, I'll have big oil caps sticking up on deck.

I'm using the potted version of A-431 for a 60 watts build with 6550 or KT88.

Any advce forecoming, will be greatly appreciated.

Thanks for looking.

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Old 25th November 2013, 04:20 AM   #2
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You can pull up to 250 mA. from a 5AR4. If that's enough for the entire stereoblock, go for it. Definitely increase, by a substantial amount, the value of the reservoir cap. used to feed the O/P tube anodes.
Eli D.
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Old 25th November 2013, 04:27 AM   #3
kevinkr is offline kevinkr  United States
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I think based on experience that you will need two 5AR4 and chokes should have twice the current rating and half the DCR of the items used in mono amp.. (Resistors halved if powering both channels) You can also double the capacitance ahead of the choke and go significantly higher than that on the rest.
"Extraordinary claims require extraordinary evidence." - Carl Sagan
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Old 25th November 2013, 07:35 AM   #4
Zekk is offline Zekk  Singapore
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I've a nice pair of Lorenz GZ32 leftover from my Fisher 100-AZ.

With a power trans of 400-0-400 @ 300mA , 4pcs. 24uf and 2pcs. Partridge 5H chokes, and parallel GZ32, how do I configure the ps to achieves a B+ of 500vdc, 420vdc and 150vdc.?

Thanks, guy!

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Old 25th November 2013, 09:15 AM   #5
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Try PSUD from Duncan-Amps.
Its a nice free tool for designing of powersupplys.
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Old 25th November 2013, 11:27 AM   #6
Zekk is offline Zekk  Singapore
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Sorry wrong info of power trans, it's rated at 400mA.
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Old 30th March 2014, 12:45 AM   #7
rdk4952 is offline rdk4952  United States
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Hi everyone, I use to own a pr of 60's..I came across this online.
Can anyone comment on the mod's done to these 60's
especially the part about the "motor run capicitor'
never heard of this before, and adding a choke'..
Thanks Bob.

EICO, unlike McIntosh, Marantz, or Fisher, isn't quite spoken with the reverent tones with discussing the best of the vintage amplifiers, but to do so would be a mistake. From their budget units, up to the the flagship model, the HF-60, they represented a serious competitor to Heath and Dynaco, offering good value for the hobbyists of yore. When I had the rare and unexpected chance to buy a pair, I went for it, knowing I would be hearing with one of the best EL34s amplifiers around.

The Amplifiers
So what is an EICO HF-60? It's a monoblock amplifier - requiring two for stereo - featuring 5AR4 tube rectification, the classic Mullard 5-20 circuit with an EF86 and 6SN7 driving EL34 output tubes in Ultralinear, fixed bias, and the legendary Acrosound TO-330 output transformer. There's nothing tricky going on here circuit-wise: current sinks, current sources, regulators, dc filaments, etc are non-existent, but component quality is still quite high with wirewound resistors, good tube sockets, and a really nice hunk of iron. Biasing is through two pots: one to balance between output tubes while the other is raw bias. These came as very basic kits with no circuit boards: the end-user was expected to be experienced enough to do point-to-point wiring.

Another thing to note is the high plate voltage and bias, making the HF-60 run steep Class A. 500VDC on the plates with 65mA means the EL34 output tubes are running 32.5Ws (plate + screen) of dissipation, right on the bleeding edge of their maximum rating. If the lights are off, a faint red glow can be seen on the plates(!) which, according to the manual, is considered normal operation! Back in the day, this was no big deal since you could pop down to the local store to pick up your new set of Mullard EL34s, but now with the high price of quality old-stock tubes, a user of this amplifier may want to dial back a few milliamps.
Note that the HF-60s are not stock. The addition of the 1.5H choke and the large motor run capacitor helps to clean up the power supply. Also the "battery bias" mod where the EF86 is biased via a 1.5V AA battery - and cap coupled - supposedly improved the treble and detail. I have, however, never heard a stock HF-60 so I cannot compare.
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Old 30th March 2014, 02:45 AM   #8
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A motor run capacitor is a comparatively rugged polypropylene/oil cap used in electric motors for phase quadrature. They're made to last in hard use, and can withstand surprising short-term overvoltages. Somes folks will use them as the first (input) capacitor in a tube amp B+ supply (including the Marantz 8b), or even for all supply caps.

They're gaining another popularity in *reducing* B+ voltage, often too high with modern AC line voltages on vintage electronics designed for 115 volt supplies and inexpensive replacement tubes. 500 volts on EL34's is seriously too high, for example. A smaller-than-stock value of input capacitance is chosen (for a practical B+ voltage), then a choke is added to keep down ripple.

All good fortune,
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Old 30th March 2014, 10:38 PM   #9
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The post you quoted - those are my HF-60s - basically done by a previous owner. I just tidied up the wiring and changed the input cap value.

If I remember correctly, After the 5AR4 rectifier, I used two 22uF/350V caps in series (with resistors in parallel to each cap), then to a 1.5H Dynaco choke attached to the side of the chassis (but still internal). The original can cap position was replaced by a 40 or 50uF polypropolene "Suzuki" capacitor. B+ - with modern line voltages - is still a high 495VDC, but that's no problem for original Mullard EL34 XF2 tubes. Shuguang EL34s - surprisingly - could also take the abuse.

The Eico HF-60 certainly was designed with no regard for tube life, but more for max power with a claimed 60Ws. Just a sign of the wattage wars of the late 50s.
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Old 31st March 2014, 02:35 AM   #10
rdk4952 is offline rdk4952  United States
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1. Chris, Thanks for a very clar explination'
2.Kstagger..how ironic is this'
could you tell me what wedsite I found your info..
just want to be sure..were on the same pg..
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