Clean HF-81 on Ebay

[NOSValves]

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1940970782

[Tom Mobley]

Craig,

I looked at that earlier. Looks pretty good to me. I don't like his limited payment options though. He did at least know what the blue thing is under there....

Tom

Incidentally, I now have a set of 3 Sprague Atoms 40, 40, 20 I was thinking to use to replace the can cap. I put put a can cap in it, I'll make somebody a smokin deal on these.

Tom

[mike stehr]

Hook me up, Tom!

I'll find uses for those caps!

I'll still take them off your hands, regardless, but what voltages are those?

[mobile homeless]

That EICO caught my attention as well but I have been trying to play the old beast down as the prices just got insane for awhile. That unit does look good and has the full manual to boot, something that is not always around these days (at least in original form).

Tom, I am still going to scan the manual but my buddy has it for the week. When it returns, it goes up.

I am really looking forward to the "Super HF-81" amps Jeff and I are building. As noted in the Post on the AE-1~Moondog combo, each of our amps will be different but will be using the same type wood base with probabably a copper top (he will powder coat his). AGain, he will focus on building an amp with dual volume pots and I am going the full integrated (with just selector/volume/on-off). There will be no balance or any other extra controls.

Figuring out how to get rid of the tone control circuit is not easy. As noted, it does make you have to drop 1/2 of the 12AU7 which WILL change the sound of the amp per say. Jean-Francois is just electing the drop the entire pre stage to make this easy. I really want to figure out how to leave it in as I think it important to the sound as well as the soul of the HF-81.

I have a step by step method for dropping the tone controls and ditching the 12AU7 half but I am not sure about whether it is the best approach. Listening to the HF-81's amp finally in a correct fashion with just a volume pot running it was more transparent but perhaps a little less body. It really relied on the output voltage and PS of the CD player at hand. Luckily the Rega Planet is a worthy contender here.

Jeff has MUCH more experience building amps from scratch, something I have never done so this will be my first. This is going to be a bit of a step from soldering and replacing parts but I have been wanting to build this for the last five years or so.

I'll share my findings with you and have been thinking of making a page for it as well (I posted that screenshot of the beginning of it with the napkin drawing of Jeff's version).

We'll see what happens. I suppose we'll share a few emails as well.

kh

[Tom Mobley]

Mike,

They are all three 500V, the 20 is a little physically smaller but not much. I just bought this Scott 222C on ebay, I've decided I want to keep them until it shows up, probably ask $10 plus $3.80 for a stamp. I just know that if I let them go before it shows up it'll need one.

Kelly,

Spent some time with my upsidedown HF-81 and the schematic, here's what I see: Looking at channel 1 (left side looking at the amp rightside up and from the front) the signal leaves the vol pot via a green wire and goes straight to the pin 7 of the 12AU7, then exits from pin 6 via one of the .1uf caps, to a solder lug and on to the tone controls through a brown wire. Signal returns from the tone controls on a gray wire which goes directly to pin 2 of the 12AU7, exits from pin 1, goes through the other .1uf cap to a solder lug and directly to pin 7 of the 12AX7. These solder lugs mentioned have two purposes, one to provide mechanical suppport to the cap and to provide a handy place to hook up that goofy tape out circuit.

Two methods of bypassing the tone controls present themselves: first and simplest, run the signal wire from the vol pot directly to pin 2 of the 12AU7, disconnecting the wire that now runs to pin 7 and disconnecting the gray signal return from pin 2. This amounts to a brute force type bypass of half the 12AU7 and the tone controls. Presently unknown is how leaving half the 12AU7 dead would affect the live half, I have someone looking into that. The other unknown is the effect of dropping half the amplification. I don't know if that first stage of amplification is more or less "soaked up" by the stuff in the tone controls or not. Which consideration surfaces the other fairly obvious method: keep the first stage of the 12AU7 and it's output cap, but instead of running the circuit from the cap to the tone controls as detailed above instead run the output signal from the cap directly to the input pin 2 of the 12AU7, again disconnecting the gray signal return wire from the tone controls. This approach retains the amplification function and capacitance of the first half of the 12AU7 while dropping out the tone controls.

I really have not enough experience with this stuff to have a feel for which method would work best, but it does occur to me that if the gain is thrown off too far by either method it might be resolved by swapping out the 250K vol pot for a 100K or 500K, depending on which way the old ball bounces.

The other channel is the same electrically but a little different mechanically because of the unwanted and unneeded "Speaker Selector Switch" which, if thrown, completely disconnects the output of the channel 2 line stage from it's output stage and instead splits the channel 1 line stage output between both channels of the output stage. Channel 2's line stage output is just left dangling in mid-air while channel 1's line stage output is suddenly split between two power amps with no compensation for the different resistance and impedence it now sees. Eico's willingness to implement this sort of brutal approach is leading me to figure that the first method given above might be OK.

Just so we're on the same page I'm using the term "line stage" to refer to the functionality of the two sections of the 12AU7 and "output stage" to mean the 12AX7 and the two 6BQ5's, which may not be technically correct.

If running only half of the 12AU7 turns out to be the way to go, the bottom of this amp would be cleaned up and simplified considerably by leaving out the caps and tone controls, the goofy "Speaker Selector Switch" and the even goofier "Tape Out" wiring.

Clear as mud? Good.

Tom (proofreading this at 3:30 AM, errors and omissions may occur, but I can't see them now)

[mike stehr]

Tom,

You might as well keep those capacitors, you'll need them down the road, trust me.

(And I was needing that 40uF 500 volt cap.)

I need to order parts anyway.

I was looking at that Scott 222c a few days ago...

Glad you got it!

Hopefully it's like the auction said, clean it up and go.

I would of went for it, but I might have a 299c.

[Tom Mobley]

Mike,

That thing looks pretty good to me. Those pics were taken in a very harsh light, maybe direct sunlight, makes things look worse that they really are. I don't care much about a few scratches on the faceplate, but what I could see of the works looked pretty cherry to me.

It'l be interesting to see what shows up, unless it's totally roasted I should be able to get out of it OK later. I though the BIN price was very attractive.

Tom

[Parrot]

I don't see any point, beyond having fun and experimenting, in radically changing an integrated amp into essentially a power amp. There are already plenty of Eico power amps to choose from.

[NOSValves]

paulparrot,

I agree completely its just not worth it. They work great in there current form if brought up to snuff !! If you want a power amp buy one. Why ruin the value of a vintage piece !

Craig

[mike stehr]

Yeah, take it from a guy who learned the hard way.

[mobile homeless]

Well, I am thinking it would be worth it and an interesting project inlcuding one fun to build on your own that will bring excellent sound good enough to match most anything.

I am taking a pair of HF-81 outputs and a power trans I am getting from a friend out West and making the HF-81 circuit no holds barred, integrated and all. It will just be totally stripped down with just switching for 2 or 3 inputs, volume, and on/off toggle. I will include the preamp stage. Parts will be all selected for musicality first with an attempt to wrangle the last bit of resolution and performance out of the design. If we can figure out a way to do the phono inboard with no compromises, it will be there.

I happen to love SET amplifiers and plan on doing another but I have the opportunity to get some transformers now and love the great performance of the HF-81 so much, I want to make it all out on a wood chassis with copper top plate, all tubes being exposed just like the Moondogs. The layout of the interior will be clean and organized with no kit restrictions. There will be no more than two knobs up front (perhaps only one with toggles for inputs and power).

I have been wanting to do this for quite awhile and am looking forward to having all new solder joints with new or NOS parts within. This piece will look as good as it sounds, both inside and out.

kh

[mike stehr]

I think Paul Parrot was mentioning taking the pre-amp circuit out of a integrated amp.

Which we all agree is not a good thing with the Eico mono/stereo HF series.

It's good to see you trying a scratch build tube project, Kelly.

Your a wealth of knowledge on the subject, I'm suprised you haven't dabbled with DIY tube circuits yet.

I'd love to cobble a DIY tube circuit of some sort, but it's a real challenge going from ground up, so to speak.

Even if it is someone else's circuit design.

To me, anyway.

I'm sure I'll eventually do it, someday...I dunno, maybe it's more of a mental block, if anything.

(I really need to do it with a RCA SE 6BQ5 amp, the chassis

sucks!)

Right now, the vintage stuff keeps me happy.

You should hunt down a good vintage example of a SE 6BQ5 amplifier, with the right speakers they do have a good sound.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

ARRGH!

I need to get my damn Cornwalls I bought from Jazman last September home.

I need to figure out what would be the best and reasonably priced way to have them picked up from his home near SF and delivered to my door, or picked up at a Depot in Spokane.

I wanted to go get them, but I can't swing it.

Doesn't FedEx frieght pick-up from one's door?

Or UPS?

Jazman suggested a national moving company like Mayflower or

United or Atlas or something, but these places have some SERIOUS rates.

I want someone to pick up the speakers at Edmond's door, so he doesn't have to deal with any or as little packing issues as possible.

He's been working the shift differential from hell, 4AM to 1PM, doing a 140 mile round commute to work and back.

So he doesn't really much time to do jack.

(Notice his lack of posts, lately.)

I don't know why I'm posting this, I should be calling around, but if anyone has any ideas they can kick me, it sure would be appreciated!

I would like to enjoy my Cornwalls before Christmas, or at least New Years!

THANX!

[Erik Mandaville]

I feel sort of compelled to offer a little bit of defense for Mobile's (and his colleague!) interest in rejuvinating, updating, (subjectively) improving, etc. a successful tube design from the past. My opinion is that science and art are strongly derivative, in that modern or contemporary approaches to design and design implementation rely very strongly on previously established groundwork, ideas, concepts; and in this case, an already highly regarded musics playback system (the HF-81).

The Wright Brother's little plane also flew, so why go any further? Certainly this is a simplified analogy, however there are some similarities, I think. Regardless of what others might perceive as a waste of time and energy trying to improve somethng that already works just fine, I can't help but respect the dreaming, thinking, planning, and so forth that goes into the creative act -- whether a sculpture or painting or music making machinery. It's what helps people grow as individuals and, even in failure, teaches lessons and provides knowledge that greatly surpasses sitting, doing nothing, and accepting things as they are. I don't even know how many times I've heard people say something like, "My grandpa always used to say, if it 'ain't broke why fix it?!" Sure, that has some sense behind it, but it's also an easy way out. My belief is that things don't necessarily have to be broken in order to be improved upon.

In working with and listening to vacuum tube (hollow state) audio equipment, we are essentially resurrecting an antiquated and obsolete technology. But many are doing this because of having the very unique opportunity of being in the position to compare and contrast currently available music playback systems with those of half a century or more ago. So newer in fact, in some cases might not be better. Nevertheless, an ACTIVE interest (one that is willing to question, experiment, and work-through by trial and error), is what can absolutely lead to really neat discoveries! Moreover, Kelly cares enough about this interesting concept to build it around a very special chassis design. I think the circuit planning and design should really be the first problem to solve, but the fact that its 'house' is already being given attention illustrates a healthy confidence in and a respect for a great tube amp. from the past.

Things like this need to be encouraged!

Erik

[Tom Mobley]

Kelly,

did you see my post above about removing the tone controls with and without dropping half the 12AU7? How does this compare with the step by step method you mentioned or you Canadian friends method?

Tom

[mobile homeless]

Tom, it's just about the same. Here is the latest from my friend in Quebec after he tried the HF-81 bypassing the ENTIRE preamp stage, IOW, running the amp section with just a volume pot. I had tried that again with my Creek and found it transparent but lacking in drive and bloom:

Now let's talk about the Super Eico.

After a sufficient period of time I can say that I prefer the Eico unaltered over the preamp bypassed tweak. I found your sonic description of your trial of the Passive in the tape out quite like what I heard.

So I'll agree with you now about the super Eico needing the preamp.

I dont know where this leaves us on the 1/2 12AU7 aspect. I can say that I dont think that running half the tube will harm the sonics at all but leaving out the other half will definitely be a difference. As for leaving both in, I am not sure about that one either.

Too bad you are getting buzzing still. Is it coming from the speakers now or just the amp itself?

kh

ps- Erik, indeed, the ole Moondog is a very vintage SET offering compared to some of the others. I would probably be trying a SET first due to the simple nature of the wiring but I just dont have the proper transformers at the moment(and we know how important they are to the sonics). I love the EICO and I know where I can acquire some, hence the timing of the whole affair.

[Tom Mobley]

Well, it's no big deal to try it both ways. The actual doing of this is really sort of trivial, the soldering needed is not even hard to get at or anything.

I'm refinishing my LS's right now, all the drivers are out of the boxes. I have the Eico hooked up to a set of 4-ohm Nakamichi car speakers just laying there out in the open, the sonics are, uh, er, "somewhat degraded" right now. I'm hoping to have the speakers back together by Tuesday evening, I'm going to go ahead and cannibalize the cherry drivers out of my 77 Heresy's to put them back together.

I amy need to recruit a set of good ears here in Phx to do before and after testing, mine are not that great or educated. Any volunteers? Audiophile ears in Phoenix?

Here's a proposed procedure:

1) listen to stock unit a while

2) bypass balance pot, trivial soldering, listen

3) if OK, bypass tone controls only, keeping 12AU7 in circuit, listen

4) bypass half the 12AU7 and the tone controls, listen

5) look at routing the (line in) wiring around the selector switch, have to check what (if any) equalization might be being applied to the line inputs on there.

Comments, criticism, suggestions?

I need to get a test tones CD and one of those Rat Shack SPL meters. Any suggestions on the test tone CD? Good disc, good vendor?

Tom

[Tom Mobley]

oops, the PS. It's just buzzes like a fluorescent light transformer. None of the stuff I've done has fixed it or even changed it. The PS buzzes, vibrates the amp chassis and there is a low level audible from both the chassis and the speakers as soon as it's turned on. I really can't hear once any tunes are cranked up, even at a low level. Get used to it, I guess. I tried all that fixit stuff you suggested in a thread several weeks ago, no joy. Doesn't really matter that much I guess, just bugs me because I know it's there. It's probably something within the transformer, but it puts out correct voltages, so WTF??

Tom

[mobile homeless]

Did you tighten the 4 transformer bolts a bit?

kh

[Tom Mobley]

Yes. There's two sets of nuts on the thing, one set holds the transformer together and are above the chassis, the other set are below the chassis on the same bolts, holding the transformer to the chassis. It was a little tiny bit of a PITA getting the ones that hold the tranny together, I basically had to loosen the transformer from the chassis and lift it a little to get an old ignition wrench under there. After all this jiggling around they weren't really loose. Dang. Still cranks out the tunes.

Calling all audiophile ears in Phoenix, FREE chance to join exciting, ground-breaking bleeding-edge project!!!!! just email tmoble@earthlink.net or respond here!!! No work, all play!!!! free beer!!!!! No more exclamation points!!!!? Offer subject to unannounced changes!!!!

Tom

[mobile homeless]

As for the power transformer nuts, they are a pain. Do you still have the non metalic washers under the screws on top of the transformer?

Be careful of Audiophile ears...a lot comes along with it that might not help such an experiment as this one. That average audiophile has not been through the whole Hi-end game and out the other side and back again. Most are still playing the game and not knowing it at the time.

Besides, I dont think there are a lot that fit either category within this forum and who also happen to be living in your area.

Your best bet is to hone your own ears and relax, listen, and see how you come along. Being exposed to other quality gear surely helps to get a point of reference but even then, there are many variables. Knowing the sound of real instruments, both electric and acoustic helps. Have a good reference system is another positive.

kh