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Trusty McShaned Eico HF87

97.95.43.235
Posted on August 15, 2016 at 00:39:10
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005









When I get back into town,I thought about converting one of my HF87s to fixed bias with a balance and bias pot per channel.This amp sounds so incredibly good tho and the EH 6CA7s are just charming.I still like the Genelec RI KT77s better however,they are much cheaper than the KT77s.Still the EH 6CA7 will run any of my XF1s and XF2s around the block.We are talking about the higher GM 6CA7s in 8300 to 8500 range.

"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

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RE: Trusty McShaned Eico HF87, posted on August 15, 2016 at 07:23:14
spindoctor
Audiophile

Posts: 1661
Location: Virginia
Joined: December 31, 2002
 Michael
This looks great and I suspect sounds even better. You've inspired me to pull out the St-40 I was given a few years ago and bringing it back. Thanks.
Sim

 

RE: Trusty McShaned Eico HF87, posted on August 15, 2016 at 07:25:21
airtime
Audiophile

Posts: 11287
Location: Arizona
Joined: February 4, 2003
 I didn't realize it used 6SN7s in the preamp section - NICE!

 

RE: Trusty McShaned Eico HF87, posted on August 15, 2016 at 09:46:15
elflow
Audiophile

Posts: 354
Location: Indiana
Joined: November 1, 2005
 Hi,
If my memory is correct the output transformers are better suited for fixed bias operation.
Using the HF89 schematic as a guide I converted my HF 87 several years ago, I felt it was a night and day improvement. Even with a Mcshane style PS. and otherwise stock HF 87 I still preferred a stock Dyna ST 70 over the cathode bias HF 87. After changing the HF 87 to fixed bias the HF 87 far outdistanced the Dyna ST70
.

 

RE: Trusty McShaned Eico HF87, posted on August 15, 2016 at 11:29:08
elflow
Audiophile

Posts: 354
Location: Indiana
Joined: November 1, 2005



If my image uploaded, you can see that every thing was securely mounted under the chassis on new brackets using existing mounting hardware, no holes were drilled and the old electrolytic caps are retained topside for a stock looking HF 87. I also used a substantially up-rated Haybor power transformer. I made each change separately and the only day and night difference was the switch to fixed bias.

 

RE: Trusty McShaned Eico HF87, posted on August 15, 2016 at 11:49:44
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 Very Nice!
Where did you get the brackets for the capacitor mounting? It looks like a spare one off a deuce. I never drill holes for modifications except on an Eico,or a Dyna St70,or some of the Heathkits.It doesn't hurt the value of those amps so much unless it's a factory built unit in great condition.I did it like the HF87 on an HF87 for three people now.



"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Trusty McShaned Eico HF87, posted on August 15, 2016 at 13:26:56
elflow
Audiophile

Posts: 354
Location: Indiana
Joined: November 1, 2005
 The inspiration for the power supply bracket is right from the Citation II, I even bought a double fuse holder to mount the PS diodes like the Citation's use. The brackets are hand formed using a large bench vise. I took it as a personal challenge to mount the brackets using only existing holes. Being than I am metric challenged when I ordered the Panasonic TS caps for the doubler I ordered the longer more slender ones instead of the short fat ones.
The amp is sort of like a base family four door grocery getter with poverty hubcaps, but under the hood it has a high performance mega cube engine. Only a sharp eye will catch the extra 3/8" of laminations on the beefed up power transformer.

 

RE: Trusty McShaned Eico HF87, posted on August 15, 2016 at 13:42:03
Eli Duttman
Audiophile

Posts: 10455
Location: Monroe Township, NJ
Joined: March 31, 2000
 Very nice work! Decent O/P "iron" along with a good PSU are excellent starting points.


Eli D.

 

RE: Trusty McShaned Eico HF87, posted on August 15, 2016 at 14:00:56
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 Keep in mind that the cathode biased HF87 makes as much or more power than the Dynaco ST70 with fixed bias..This is because the HF87 is running a higher B+ potential, between the plate and cathode of the output tubes.You then have a far superior driver/phase-splitter,and voltage amp,then the 7199 offers.You have two sections of the 6SN7 in each channel along with the voltage gain of the 12AX7. Once the McShane upgrades are done,this amp takes off and flies around the room.I have never gotten the dynamics,depth,or bottom end in an ST70,that I have gotten out of HF87 even with cathode bias.Even the iron as you say,is so much better in the HF87.
What the fixed bias will do is give me more power because now you will have full plate voltage running across the output tubes.I will also be able to run KT88s,KT66s,and 6L6gcs as well..
The original cathode bias resistor was 235 ohms at 10 watts..The other side was a 165 ohm in series with the 12AX7 filament to make up the bias resistnce on the other side.I used a 250 ohm on both sides and then put 6.3vac on the filament of the 12AX7 between 4,5,and 9.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: Trusty McShaned Eico HF87, posted on August 15, 2016 at 17:12:34
elflow
Audiophile

Posts: 354
Location: Indiana
Joined: November 1, 2005



Thank you for your kind words. The HF 87&89 use a fifty ohm 10 watt resistor between the voltage doubler caps and the B+ filter/storage capacitor do you have a recommendation for a specific choke to replace the resistor, or any other ideas to reduce the ohm value of this resistor to reduce the DC resistance of the power supply?

 

I put in a choke in place of the 50 ohm resistor, posted on August 15, 2016 at 17:28:02
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 like what's in the Mac Mc240 and the Citation 2.Now I had a 50 ohm choke in there at 1hy.I took it out and put in a .5hy at 30 ohms..The B+ went up 2.3 volts.having a choke there really improves backgrounds,clarity,and overall control of the amplifier.I'm going to use the HF89 bias scheme and the reason I like the older bias schemes where they use a balance and bias pot,it is so much easier to bias because you aren't chasing the bias so much.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

RE: I put in a choke in place of the 50 ohm resistor, posted on August 15, 2016 at 17:50:25
elflow
Audiophile

Posts: 354
Location: Indiana
Joined: November 1, 2005
 What is the current capacity of the choke you used? I have never measured the voltage drop across the 50 ohms to see how much current is flowing.

 

RE: I put in a choke in place of the 50 ohm resistor, posted on August 15, 2016 at 18:34:20
Michael Samra
Dealer

Posts: 36118
Location: saginaw michigan
Joined: January 30, 2005
 300ma on the .5hy at 30ohms and the 50ohm choke was 1hy at 240ma.Those low Mu and low DCR chokes have a an effect on low level resolution that can't be denied IMHO.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken

 

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