HK Hot Rod nears restoration completion

[audiodon]

Well this integrated has now had a good 80 hours of ripening time and is coming along quite nicely.
There are a few things left to do and I'll list something I've done.
To do:
1. The power tranny still buzzes a bit, even though the AC on the primary side has been dropped by thermisters to about 117. I'll have to give it a shellac bath sometime.
2. I'm really considering changing out the 12AU7s for 12BH7s. I've been told that I'll have to change the way they're powered between pins 4&5 and 9, but that's doable.

I played with 12AX7 preamp tube substitutions.
Sylvania gold brand triple mica 5751s: Vocals and solo instruments way up front and centered.
RCA triple mica black plate 5751s: Vocals and solo instruments up front, nice detail in complex passages and heavy orchestrations.
GE triple mica black plate 5751s: Vocals and solo instruments not quite as far up front, but the backgrounds are absolutely crystal clear.

This was the first time I'd tried these three in a non-Fisher integrated amp or receiver. It finally illuminated something I wasn't quite sure how to articulate.
Part of the Sylvania magic as listed in Joe's tube lore is that they accentuate solo instruments by smearing the background a bit.

I'm having a lot of fun.
I do have to say that this HK now rivals some of my best pieces. It's a close contender to my Fisher X-101-C and my best Fisher 500-C. That's saying something.

 

[nate86]

Wow; that project has come a long way. It looks great!

Nice work!

 

[GordonW]

2. I'm really considering changing out the 12AU7s for 12BH7s. I've been told that I'll have to change the way they're powered between pins 4&5 and 9, but that's doable.

Naw, man, it's not that hard! The 12BH7 has exactly the same pin-out as the 12AU7! Should be no problem, just dropping them in. As long as you have the heater power for another 300ma @ 6.3v over the 12AU7 (and I don't think that's going to be a problem with an HK power transformer), it'll be fine.

It's the 6CG7 and related types, that require rewiring pins 4/5 and 9 (the 6CG7 doesn't use pin 9, and requires 6.3v between 4 and 5)...

So, just drop in a 12BH7. I know it kicked butt in the Heathkit W5 (in the diff-amp/output driver position- the second of the two input tubes). That's what I'm going to be using in my Magnavox 6L6 integrated I've been posting about here, too...

Regards,
Gordon.

 

[audiodon]

Well, I thought I had a lot of 12BH7s. I don't. I have a few though.
I spent the workday rolling:
RCA clear top 12AU7
RCA black plate 5814
GE gray plate triple mica 5814
RCA 12BH7s.
I really liked the dynamic nature of the 12BH7s.
After some research, I decided that, since I had about 20 of them, I'm curious about trying them.
I'll open a new thread on that because it might be of interest to many readers.

It may all be for naught. I don't use the rumble or scratch filters or the tone controls. There's a switch to defeat the tone controls, so we may just be looking at a gain stage.

http://www.audiokarma.org/forums/showthread.php?t=423325

 

[audiodon]

Well, here's what I ended up doing:
1. Ended up putting in a 6CG7 instead of a 12BH7 in that 12AU7 slot. So both 12AU7s are now replaced with 6CG7s and are powered from the same AC filament supply.
2. Extended the AC filament supply from a 7247 to the 6CG7. Saw only a .1 voltage drop across the 6L6GCs from this change.
3. Put two 150 ohm 5 watt wirewound resistors in parallel to make a 75 ohm load resistor in the DC filament supply, boosting it from 11.6 to 12.3 or 12.4 for the two remaining 12AX7s running on DC filaments.

I think I'm going to need a bigger wattage 75 ohm power resistor because these two get too hot.

The power transformer still has a mechanical buzz and the system has, and always had, some hum I've still got to chase down.
There's a bit of (likely) 120hz audible hum on both channels, barely noticeable. I thought the power supply upgrade of all electrolytics and changing out all diodes would fix that but no dice.
Additionally, there's a subliminally audible hum on one channel only that is volume dependent.
Left to do:
1. Replace the two remaining ceramic capacitors (labeled 2k on the schematic and .02 on the cap) with .022 orange drops.
2. Chase down the single channel hum.
3. Chase down the power supply hum.
4. Eliminate the mechanical noise.
5. Enlarge wattage rating on 75 ohm DC filament load resistor.

This is the first time I've done this comprehensive an update.
All suggestions on how to chase down and eliminate the hums are welcome. For 4, I'll do my shellac bath, but I'd like to do that after it's hum free.
Don

 

[slow_jazz]

Nice job there.

 

[audiodon]

Went back at it for a while this evening.
While straightening out and putting printed out threads in a notebook, I read a post that said that the 6CG7 shield is not connected and hence the 6CG7 acts as a 6FQ7 unless you ground pin 9. I grounded pin 9 on both 6CG7s and the hum seems to be less.
I also noticed that I'd not completely flowed a solder joint on the AC filament. The top of the joint was fine, but the bottom of the joint, where the super-thin filament wire was, was unsoldered. The filaments for the two 12AX7s had one end not soldered.
I'm tired now so I'll have to figure out whether it still hums or not tomorrow. I'm guessing yes, but only part of the hum will still be there. I'd also bent some small-signal tube pins over. I'd moved them straight up during the restoration, but didn't splay them down @45 degrees again.
Here's to hoping. :beer:

 

[audiodon]

Toast or not, the buzz did not go away.

Somebody's been at this transformer before. The bolts are overtightened and a lock washer was completely out of shape. I'm going to have to replace the transformer bolts that hold on the bell housings and hold the transformer to the chassis.

So, I've removed the transformer. I kept the bolts for sizing of the replacements.

Check out the quality of these windings . . . just like that Citation II power tranny. Clearly made by the same company. Amazing windings.

Off to the shellac pool for a dip.

 

[audiodon]

This power transformer is going to have to visit Heyboer for a go-through.
I've made my first transformer mistake.
After a 48 hour shellac soak, I brought it out to the garage, which is not attached to the house, tucked the wires under the transformer and shoved it into the toaster oven to bake.

I headed back inside. Within two minutes, my wife came home from an appointment and said, "Hey, do you know there's a fire in the toaster oven out in the garage?"

My first question was, "Is the garage door still open?"

So I headed out, tipped it out of the oven got the flames out but the covering on the wires got burned off in some places. I was very fortunate and learned a valuable lesson about watching these things. Not a major fire, but destructive enough for me to realize it's now beyond my skill level to fix.

Note to self: Cloth covered wires are flammable. Be careful. Every other transformer I'd done, and there have been at least ten, had plastic covered wires. I also guess I'll be putting the toaster oven outside in the future.

 

[chinacave]

Wow Don - sorry to hear that, and VERY glad you still have a garage / house etc!

Good luck W/ Heyboer. I am curious to hear about your experience and impressions of their work.

-Ian

 

[FalconEddy]

I Should have said something. . .

You know, I saw all those great close up photos, and I said to myself. . .Don wouldn't try to cook this one to quick set the shellac it, would he?

You can sometimes get away with it if you set them really low. Although even THAT didn't work for my brother-in-law.

He toasted his cloth-wired leads the exact same way late at night in his basement workshop when my wife and I were over to his house in Vermont for a visit in early September 1989. Of course, he'd been pounding down Budweisers all day. :yes:

It scared the crap out of my wife and I when those damn smoke alarms went off, mostly because we had only been married for a couple of weeks, and uhhh well...

We couldn't even see down the basement stairs due to all the smoke created from that transformer burning in the toaster oven. And my brother-in-law was passed out in bed during this entire event. We really didn't know where it was, so we had to find it, because we couldn't wake him up. After we found it and got things under control, my wife finally got him shaken awake and was yelling at him pretty good, I told her not to waste her breath and wait until morning rolled around. I hadn't ever seen her that pi$$ed off before, but I should have known it was possible since she's Irish, a redhead, AND a Scorpio!

Actually, I think she was the most upset about being interrupted than having alarms going off, smoke in the house, and a fire in the basement. Man, you should have seen her shaking the crap out of him to wake him up. It was kind of frightening... that's how mad she was. :gigglemad :yes:

. . Falcon

 

[audiodon]

I was rushing it trying to have it ready for Saturday.
That oughta learn me. Yeah, I was foolish . . . and lucky.

The oven is at the same temperature it was for all the other transformers I've done. I only use this toaster oven for that one purpose. It's the cloth leads that got me. One lead might have shifted out from under the transformer on the tray and hit against the element.
I'd chosen this toaster oven because both the bottom and top electrical elements are shielded. I've never seen a red heating element ever in it. It's set for 150 degrees on warm. I'm convinced that the cloth lead had a hair or something that somehow got ignited. There are holes in the shield, probably to let the heat through evenly for convection.

Somehow I've always found that admitting my foolishness makes it less painful and I'm able to learn and move on more quickly. Others have interpreted my admissions as weakness and I've suffered jokes. But you can tell a lot about people by how they treat you when they know something is embarrassing to you. At almost 55, I've had plenty of learning opportunities. At this point, the mistakes are uncommon.

I used to work for man who told how he had an arrest record. He said he and his friends got the brilliant idea to drive around with someone in the trunk of the car with their hand sticking out on Halloween night. This was in the late 1950s, but he said something that I have used throughout my life rather than using elaborate concealment, lies and obfuscation in cases where fault or my own shame might be involved.
He said, "If you tell the truth, you'll never have to remember your story".

 

[awise1961]

Good point Don,

I learned a long time ago that honest people can't lie because they remember only the truth and can't remember the lie when needed to repeat it.
The dishonest man not only remembers the lie, but makes it the truth in his own mind.

Enough deep thoughts for tonight, it's back to The Band on vinyl.

Al. Wise

 

[buglegirl]

Don,

Far from a weakness. Maybe you admitting this here like a Man means someone else looking for a How To on stopping transformer buzzing does not burn down a house and even worse hurt him/herself or someone else.

I don't even leave a soldering iron unattended hot. But I have too many things around here that could get into something like that.

I did almost burn down my kitchen at Thanksgiving making Chex Mix. Seems you should not go to the computer while melting butter on the stove top for the mix.

I had a full blown fire extinguisher moment there and a massive panic attack at first.

Hint .. never put burning flaming pot of butter and Chex mix spices in sink. (No I was not dumb enough to turn on the water) Just almost caught the drapes over the sink on fire as well.

So there is my moment for the last few months.

Frannie

 

[Khodabear]

If you cop to it they have to forgive you.

Thanks for a very informative thread!

 

[Wharfcreek]

Don,

As I started reading your thread I was all hyped up on what a great job you'd done with your refurb.....painting the transformers.....new caps, buying every resistor on the shelf at radio shack and installing them all in the amp. I'm a big fan of the old HK stuff.......I find it's a good blend of the warmth and depth that you get with Fisher and Scott, but has the accuracy and definition of some of the Sherwood and Mac stuff!! Anyway......I was ready to hear how the house burned down as I read about the flames!!! WOW!! I know the feeling! I almost burnt down my house once......not with electronic gear, but I was static-timing a motorcycle....waiting for the points to 'open' so I could set the ignition. Had the plugs out of the cylinders....and when the damn points opened, the plugs sparked and ignited some fuel vapors around the carb, started the carbs burning, which immediately burned through the gas-tank balance tube. Burning gas all over the place....and me thinking the tank would explode any moment. I ended up Lassoo'ing the bike with a garden hose and dragging it from the garage to the driveway to 'let 'er burn'!! Drew a crowd in the neighborhood, as I'm sure you can imagine!! Strange how some accidents happen.....and how, in afterthought, they can be prevented. Anyway, I've been working with Phil at Heyboer on both Output and Power Transformers for some Fisher units. He's a great guy...and I'm sure will be able to help you with this HK unit. Good luck!! Tom D.

 

[FalconEddy]

I was rushing it trying to have it ready for Saturday.
That oughta learn me. Yeah, I was foolish . . . and lucky.

The oven is at the same temperature it was for all the other transformers I've done. I only use this toaster oven for that one purpose. It's the cloth leads that got me. One lead might have shifted out from under the transformer on the tray and hit against the element.
I'd chosen this toaster oven because both the bottom and top electrical elements are shielded. I've never seen a red heating element ever in it. It's set for 150 degrees on warm. I'm convinced that the cloth lead had a hair or something that somehow got ignited. There are holes in the shield, probably to let the heat through evenly for convection.

Somehow I've always found that admitting my foolishness makes it less painful and I'm able to learn and move on more quickly. Others have interpreted my admissions as weakness and I've suffered jokes. But you can tell a lot about people by how they treat you when they know something is embarrassing to you. At almost 55, I've had plenty of learning opportunities. At this point, the mistakes are uncommon.

I used to work for man who told how he had an arrest record. He said he and his friends got the brilliant idea to drive around with someone in the trunk of the car with their hand sticking out on Halloween night. This was in the late 1950s, but he said something that I have used throughout my life rather than using elaborate concealment, lies and obfuscation in cases where fault or my own shame might be involved.
He said, "If you tell the truth, you'll never have to remember your story".

Hey, I don't think you were foolish at all. And I apologize if that's where it sounded like I was headed. As I said, you can generally get away with it on a low temperature, which you did, plus you tucked the wires safely underneath like you're supposed to. I was just referring to a situation for my brother-in-law where it was there for a long time unattended where it didn't work, I was going to say something about it, but I didn't. . .until later.

At family gatherings, twenty-some years later, in the NEW house he built, we'll occassionally mention that event when he goes to use a toaster oven. We never mentioned everything 22 years ago the next morning... just the transformer/toaster oven fire part.

* * * EDIT * * * By the way, this amp looks, "Impressive, MOST impressive"*, from where it started out.

* Darth Vader, Star Wars: Episode V - The Empire Strikes Back (1980)

. . Falcon

 

[audiodon]

Thanks Dad.

Link to the "Luke I am your Father" graphic from Star Wars lost.

 

[steph_gaynor]

hey sorry to hear about this don,

but thankful it was not worse.

Stephanie

 

[audiodon]

Got the power trafo back from Heyboer today, along with the power trafo for the Masterpiece Citation II.
One thing at a time though. As my user title says, no more multitasking. These'll have to wait their turns.