Eico HF 60 Advice

R

R Robinson

New Member
I just fell into an Eico HF 60 in pretty good shape. Its never been recapped. Before starting it up I took out the selinium rectifier and put in a diode and changed out one electrolytic that was way over. I started it up slowly and everything was pretty good until about 70 volts. Then I started getting a hum out of the transformer. Is this normal for Eicos? Could it be the diode? I put in a 1n5408 diode. Is that overkill? Could I have possibly put it in wrong ( I put the band towards the transformer feed) ? The bias was a bit high at full voltage but I was able to get it down to -40 volts (the manual recommends -47). Should I just go forward and recap it? I wanted to test it to make sure there was nothing severely wrong. That it was worth the time and effort. This will be my forth tube recap. I have a Fisher 400 and
Dynakit St70 but couldnt resist getting my hands on this Eico.




IMG_5850.jpgIMG_5864.jpgIMG_5848.jpg
 
Register to hide this ad
O man, I'd be getting rid of all those (very likely quite leaky) paper caps, aged tubular electrolytics, and can caps before I put any more electricity into it! Humming PT usually indicates excessive current draw--my bet is bad electrolytics. The 1N5408 is OK--the cathode band should point toward the transformer for a negative bias voltage. Further live "testing" could result in damage to the transformers so, yes, re-cap now. Nice amp!

Resistance check the transformer windings: power transformer and the output trans.

Dave
 
Okay I put in new caps in and it sounds great. The hum from the transformer is gone. Also replaced four 100k resistors that were out of spec. Its a solid amp. A very slight him from the speaker but its less than the background noise in recordings I've played. Any suggestions on bias? In the brochure it recommends -47. Right now Ive got it set at -40 which is about 20% less and seems to be in line with what I have my Dynakit 70 tubes set as per the Roy Mottram upgrade. The Eico is a very nice amp.
 

Attachments

  • IMG_5899.jpg
    IMG_5899.jpg
    165.3 KB · Views: 36
Regarding the bias, i believe that eico’s spec was already hot: class a operation…65 mA or so. So, if you are running less negative grid bias, those tubes are probably screaming. Are those the original sylvannia / mullard 6ca7 in there? If so, those are tough tubes but you are advised to still properly adjust the bias. It’s better to get an actual plate current / plate dissipation from the tube than just the grid voltage. Although i wouldn’t run the amp any more in this condition, Looking at the tube plates in the dark will tell you a lot based on their color. Slight dull red is ok, but not much more. It sounds like you are have a problem with your bias circuit. Changing to a silicon rectifier should give you MORE negative bias voltage and allow the amp to run cooler. If you don’t have enough range in the bias / balance pots to bring the bias in range, there is something wrong. First, try extensively cleaning the bias / balance pots. This has been a necessity on other eicos ive seen. Measure the pot resistance after cleaning to make sure they are working in spec. Check for resistors drifting high in the bias network. Replace the bias electrolytics. Start there and please have some kind of current limiter / voltage reducer for this kind of work. We don’t want to see dead acrosounds around here.
 
Not to be rude, but I don't like how you have those caps just sitting there soldered to the end of a wire. You should do more reading and do a proper restoration. I have had amps like this come to me and I shake my head as how they haven't shorted out.
 
RJB, The caps are all replaced. As are about half of the resistors (all that measured bad). No red platting that I can see. Looks pretty much like my Dyankit. But I think you're right about the pots. I've cleaned them twice but they could use another cleaning. They were pretty stiff at the beginning. And yes I have an 12amp variac. I think the danger is mostly past. Danno, yes I need to do better with the wires. Theyre pretty stable via the ground bolt connection but even since this picture was taken I've started covering the positive ends. The cans were both bad and I didn't want to purchase new cans before I knew if the amp was worth it so I bypassed them. I've kept the old cans in just for show. I plan to go back in and clean things up. Might even try the Gillepsie mod as I have some 6550's Id love to throw in. I wasn't looking for this amp, it found me. I really didn't know anything about Eico when I started.

One question, does anyone put inrush current limiters in these things? I've done it with my Fisher and thought I might throw in a 3 amp inrush limiter that I have on hand. In addition to protection it lowers the voltage to about 117.
 
It was running at about -43 dc volt when I last checked/adjusted. Down a bit from the recommended -47 dc volt recommended in the manual. It measured and seemed to be running a bit cool. That adjustment was pretty straight forward but I was having problems with the balance adj. I now realize that the balance pot is bad which seems to explain things. I imagine that the bias pot should probably be replaced too. I've tried doing a combination of contact cleaner and deoxit and will wait to see after it dries. But I think they'll need to be replaced. That said, biased at -43 the Eico sounded very good. Certainly an inspiration to go forward. Even with my cheap advent it was pretty breath taking.
 

Attachments

  • Screen Shot 2025-01-26 at 1.30.50 PM.png
    Screen Shot 2025-01-26 at 1.30.50 PM.png
    14.2 KB · Views: 7
Ground control to Major Tom:

I don’t want to come off as rude but i need to try to get through to you here because the help that has been offered to you previously clearly isn't getting through.

Please stop messing with this classic and rare amplifier until you garner some basic understanding!

1. You need to understand that your grid voltage measurement is hardly meaningful because of the variance in tube characteristics: We need actual tube plate current measurements in mA at a given plate voltage! A grid voltage measurement is not sufficient. Please take the time to learn how to measure the actual plate current of each tube and then report those results along with the plate voltage that was measured at.

2. - 43V grid voltage is not "colder" than -47V!!!!. Your amp is running HOTTER than spec!!!! Please learn how a fixed bias system works!!!
 
danno2000 said:
Not to be rude, but I don't like how you have those caps just sitting there soldered to the end of a wire. You should do more reading and do a proper restoration. I have had amps like this come to me and I shake my head as how they haven't shorted out.
Click to expand...
Did you ever redo your caps as suggested by Dan? You don’t want leads flying around loose in the chassis where they could short to chassis. A couple of terminal strips could be added to secure the caps. These are all people trying to help. We are dealing with 600v.
 
Looks like he peace'd out after being scolded! I haven't had my 60's in rotation for a while since getting the EFB hf-87...need to give them a listen soon, considering I sold mc30's to keep them!
 
I used to be the guy getting scolded and still sometimes am. It’s not fun getting your hard work bashed. I think there’s a right and wrong way to offer someone advice. But nothing was disrespectful in this thread that I see. All helpful suggestions. From top ak tech members.
 
So anyway its up and running well. A couple points. Regardless of how high regard you have for this amp, it was designed as a kit amp for hobbists to put together. Its a simple mono amp with extensive instructions on how to put it together in the manual. In the manual it isnt even expected that you be able to read a resistor. Its supposed to be fun. I respect your knowledge but you ignored my questions more than once so I went back to the manual. My question was, is it worth it to spend the time and money to rebuild? I didnt want to embark on a senseless expensive journey. If I were to advise someone on this amp I would tell them that the amp has serious ground problems due to its build. It doesnt ground easily. My first step should have been to redo all the grounds. The hum from my amp at 70 percent voltage was because of a intermittant short in the bias ciruit that caused power problems. This led me to discovering a host of other intermittant shorts. Im not an expert nor do I want to be.
 
You must log in or register to reply here.
Back
Top Bottom