More Amp Construction

MikeyFresh

Moderator
Staff member
How do I get myself into these situations...
View attachment 35882
I notice the AC outlet at the bottom of your photo has a nice scorch mark on it.

When I bought the house I currently live in, there was an AC outlet in the living room that looked pretty much exactly like that. I watched as the home inspector I hired tested it along with all of the others in the house, and when I asked him about it he just shrugged and said, "it works".

I actually left it that way for a time after moving in, then eventually got tired of looking at it and replaced it for cosmetic reasons, but I still have it in a box somewhere and will always be left to wonder what the previous home owner did to cause that to happen, but the fire retardant in the plastic formulation worked.
 

paulbottlehead

Active Member
A piece of solder swung down and briefly bridged the hot and neutral on that outlet. It's really weird because what's visible is actually inside the outlet cover material. I've left it because it's kind of funny, but I would definitely replace it if I put the house on the market!
 

paulbottlehead

Active Member
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A local guy brought over this HK250 for me to look over, and also because one of his GL KT-66s was dead (I sold him a spare I had sitting around for $10). I noticed that it had been somewhat refurbished, but the original can cap was still wired in, and the capacitors for the voltage doubler weren't the same, nor were they even labeled with a brand name, capacitance value, or voltage rating! I also get cranky when I see metalized polyester coupling caps and metal oxide resistors in the signal path; there just isn't any reason to cheap out like that.
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I put in F&T axial caps for doubler duty, and they really fill that space nicely. The old can cap was yanked out and a new cap from Hayseed Hamfest stuck in its place. This should be a real game changer for the resale value of this amp, as that new cap is super obvious. I pulled out just about every resistor and capacitor in the driver stage and replaced them all. With resale value in mind, I went with Orange Drops and lots of Vishay CCF and RN55D resistors. The old rectifier diodes came out and UF4007 diodes went in their place. The old can cap was a 20uF HV cap and the other half was a 50uF cathode bypass cap for the output stage. I moved the cathode bypass cap closer to the output tubes and used an Elna Silmic II there, then the new can cap's three high voltage sections were sufficient to replace the high voltage axial caps that used to reside inside the chassis.

I'll try to talk the owner into a 3 wire power cord before I send it home!
 

paulbottlehead

Active Member
A long time ago I bought some weird old school Bottlehead amps on Craigslist and turned them into my current pair of B-glows. I did keep the wood bases for them though, and I built a set of Paramours for the old product archive on these bases.
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The bases already had IEC power entry jacks installed in the wood, and I also put the speaker posts back there to free up some space.
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I really like that someone was doing random calculations and doodled them into the wood, and that's ultimately why these bases didn't end up in the trash can. It's good to have stuff like this around to demonstrate what kind of a difference iron can make, as the base model Paramour didn't have a whole lot going on down low.
 
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paulbottlehead

Active Member
It was also time to make a new pair of 811A amps.
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I have done a fair bit of purple powder coating and I did up a pair of plates in this nice dark textured purple, and I had leftover purpleheart wood from another job, so it was all here and waiting for me.
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There's not a whole lot going on in these.

The last pair that I have are Chevrolet orange and I'll leave the transformers blue. The sides will be marine grade ultra white HDPE.
 
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Lovely work Paul. I think I've said this before: I'm impressed by how neat, yet compact, your builds are. Great stuff.
 
There is a pair of Meanwell SMPS in there used for heating the 845s. I can do this with linear supplies off a 12V winding, but it works best to use a pretty hefty filament choke to do that. The switchers are regulated and pretty durable. I even had a tube failure recently where the grid of an output tube melted onto the filament and the SMPS survived and shut itself off in the process of the failure which I believe saved the amp from sustaining any damage.@p

There is a pair of Meanwell SMPS in there used for heating the 845s. I can do this with linear supplies off a 12V winding, but it works best to use a pretty hefty filament choke to do that. The switchers are regulated and pretty durable. I even had a tube failure recently where the grid of an output tube melted onto the filament and the SMPS survived and shut itself off in the process of the failure which I believe saved the amp from sustaining any damage.
@paulbottlehead Hey Paul what kind of Filament choke you use. Are you using a Common mode choke? What will be the correct value?

Thanks
 

paulbottlehead

Active Member
For a filament choke doing choke input duty, I use PSUD to simulate the supply to figure out what value will work properly to achieve the correct output voltage by trying the standard values in the Hammond catalog. There is no one choke that will just work for everything.
 

Wntrmute2

Not So Mediocre Member
It was also time to make a new pair of 811A amps.
View attachment 36192
I have done a fair bit of purple powder coating and I did up a pair of plates in this nice dark textured purple, and I had leftover purpleheart wood from another job, so it was all here and waiting for me.
View attachment 36193
There's not a whole lot going on in these.

The last pair that I have are Chevrolet orange and I'll leave the transformers blue. The sides will be marine grade ultra white HDPE.
Can you share a little more regarding the circuit? I'm looking for my next build.
 
For a filament choke doing choke input duty, I use PSUD to simulate the supply to figure out what value will work properly to achieve the correct output voltage by trying the standard values in the Hammond catalog. There is no one choke that will just work for everything.
Thanks
 
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