Maxxarcade
Active Member
I got the cover from Antek when I got the transformer. Unfortunately it is a prototype design, and needs some tweaking to fit the larger 3T325 that I'm using.
I hope to have updated pictures of the chassis in a couple days.
My 6L6GC amp build thread
- Thread starter Maxxarcade
- Start date
I got the cover from Antek when I got the transformer. Unfortunately it is a prototype design, and needs some tweaking to fit the larger 3T325 that I'm using.
I hope to have updated pictures of the chassis in a couple days.
Maxxarcade
Active Member
Will I have problems with noise if I place the DC choke too close to the preamp tubes? There are only a couple spots that it will fit underneath the chassis:scratch2:
If it was a swinging choke (no cap between it and the rectifier) I wouldn't put it near a preamp tube. You can have dozens of volts of AC across one of those, due to the "varying DC" voltage from the rectifier!
However, in this case, since it's a "normal" choke (i.e, the ripple has been "stabilized" by a cap before the current gets to it from the rectifier), the AC voltage across the choke is going to be pretty low. IIRC, in the PSUD2 sim, isn't the AC voltage across the choke less than 1 volt? Not much way for that to radiate anything...
Regards,
Gordon.
However, in this case, since it's a "normal" choke (i.e, the ripple has been "stabilized" by a cap before the current gets to it from the rectifier), the AC voltage across the choke is going to be pretty low. IIRC, in the PSUD2 sim, isn't the AC voltage across the choke less than 1 volt? Not much way for that to radiate anything...
Regards,
Gordon.
Maxxarcade
Active Member
Looks like 35-40v to me. I would use a 100uf cap before the choke, but I've spent way too much on shipping making all these small parts orders:yes:
BTW Gordon... Is that one of those big Seeburg speakers in your avatar? I think we have two pairs of those in our storage unit. My boss was talking about bringing a pair back to the shop and trying them out on my Maggie 175. I wonder how they would sound?
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40 volts isn't a huge amount of voltage. It'll be less interference potential than a power transformer, naturally.
I wouldn't put it right next to the input tubes... other than that, you should be fine, anywhere else.
As for the avatar pic: Yep, that's a modded Seeburg. Got them with nothing inside. Custom reconed (I picked out the cone, dustcap and spider for best performance with the cabinet and crossover) JBL M115-8A woofers, Nippon America horn with Selenium D210Ti horn driver, MB Quart 19mm titanium dome supertweeter, and a custom-built crossover I designed and built. Outrageously entertaining speaker. Will play ANYTHING without strain, and sounds quite good doing it.
BTW: I have a whole second set of the same drivers, crossovers and such. Other than the wood panels I cut out to mount the new horn and the supertweeter in the space of the original horn cutout... I mean, EVERYTHING. Had a guy here who was going to have me build him a pair, but he bailed...
As for trying the Seeburgs on the Maggie 175- I'll put it this way- with my modded units, we couldn't find an amp that was small enough to NOT work with them! Even 5 watts per channel would boogie! I'd expect a stock Seeburg to be somewhat close to as efficient...
Regards,
Gordon.
I wouldn't put it right next to the input tubes... other than that, you should be fine, anywhere else.
As for the avatar pic: Yep, that's a modded Seeburg. Got them with nothing inside. Custom reconed (I picked out the cone, dustcap and spider for best performance with the cabinet and crossover) JBL M115-8A woofers, Nippon America horn with Selenium D210Ti horn driver, MB Quart 19mm titanium dome supertweeter, and a custom-built crossover I designed and built. Outrageously entertaining speaker. Will play ANYTHING without strain, and sounds quite good doing it.
BTW: I have a whole second set of the same drivers, crossovers and such. Other than the wood panels I cut out to mount the new horn and the supertweeter in the space of the original horn cutout... I mean, EVERYTHING. Had a guy here who was going to have me build him a pair, but he bailed...
As for trying the Seeburgs on the Maggie 175- I'll put it this way- with my modded units, we couldn't find an amp that was small enough to NOT work with them! Even 5 watts per channel would boogie! I'd expect a stock Seeburg to be somewhat close to as efficient...
Regards,
Gordon.
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Maxxarcade
Active Member
It's pretty much ready for paint now.
I'm debating whether or not to install a brace across the chassis to support the weight of the transformers.
I can't drill the holes for a couple of the terminal strips until I start building it, because I'm not sure where they will need to go yet. Though most of them will be on standoffs that are attached to the tube socket screws.
Also added the holes for the balance pots, which are between the 6L6GC's just like the original HK-250. I was going to leave them out, but I decided to go ahead and install them in case I ever tube roll. I have some real nice Clarostat industrial POTs to use.
Got the stupid tape monitor LED hole slightly off center :-(
I'm debating whether or not to install a brace across the chassis to support the weight of the transformers.
I can't drill the holes for a couple of the terminal strips until I start building it, because I'm not sure where they will need to go yet. Though most of them will be on standoffs that are attached to the tube socket screws.
Also added the holes for the balance pots, which are between the 6L6GC's just like the original HK-250. I was going to leave them out, but I decided to go ahead and install them in case I ever tube roll. I have some real nice Clarostat industrial POTs to use.
Got the stupid tape monitor LED hole slightly off center :-(
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Maxxarcade
Active Member
Some progress:
thefragger
Certified Crazy.
WOW!
I freakin' love the colour!! That looks fantastic, great update.
Screws or pop-rivets?
I freakin' love the colour!! That looks fantastic, great update.
Screws or pop-rivets?
Maxxarcade
Active Member
Screws; 6-32 x 1/2" Stainless. This gives ability to also add standoffs that hold terminal strips. That way there is less holes in the chassis for a cleaner look.
The color is RAL 2004 powder coat, I think it's called Chevy Orange. Goes great with the bright blue of the Edcors, and the black aluminum knobs.
I'll try to get more pics up this weekend, since I have a couple days to work on it for once:thmbsp:
Maxxarcade
Active Member
My thoughts exactly. I wish I didn't have to wait until near last to mount the OPTs. I wanna see how it looks.
thefragger
Certified Crazy.
Chevy orange! I thought I've seen that colour before :thmbsp:
Maxxarcade
Active Member
Here's what it will look like with all the actual tubes. Only thing missing right now is the input selector and the PT cover. I can't wait to wire this beast:drool:
The PT cover will be black.
This thing is HEAVY too... probably over 30LBs.
This was taken with my other camera, so the color looks a bit different from the last shots.
The PT cover will be black.
This thing is HEAVY too... probably over 30LBs.
This was taken with my other camera, so the color looks a bit different from the last shots.
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Maxxarcade
Active Member
Power amp circuits are done.
Next I will start on the power supply so I can connect the B+ lines. I'm hoping to test the power amps tomorrow night if everything goes well.
Will a 220uf cap be enough to bypass the 6L6GC cathodes, or should I use a bit more? The original HK-250 only had a 20uf I think.
Next I will start on the power supply so I can connect the B+ lines. I'm hoping to test the power amps tomorrow night if everything goes well.
Will a 220uf cap be enough to bypass the 6L6GC cathodes, or should I use a bit more? The original HK-250 only had a 20uf I think.
Maxxarcade
Active Member
Well, I powered up the amp tonight and the outcome is not good so far. I have a loud motorboating about 30Hz or so on the left channel. I'm hoping it's just reversed OPT primaries, or something with the NFB.
The other big problem... The wiring diagram for the Antek 3T325 seems to be wrong. I used the two separate heater windings with one on each channel of the amp, and when I bring it up on the variac, I get a lot more voltage on the brown and orange pair than I do on the other pair. Good thing I didn't go over 50V on variac, or I would have toasted my new tubes with 12 volts on the heaters.
The other big problem... The wiring diagram for the Antek 3T325 seems to be wrong. I used the two separate heater windings with one on each channel of the amp, and when I bring it up on the variac, I get a lot more voltage on the brown and orange pair than I do on the other pair. Good thing I didn't go over 50V on variac, or I would have toasted my new tubes with 12 volts on the heaters.
Maxxarcade
Active Member
OK, I did another quick test before I head off to bed.
I pulled the tubes on the left channel, which did indeed have a 12 volt heater winding connected to it.
I was then able to bring the voltage up on the variac, and got audio through the right channel before it fully warmed up and started oscillating. I'm going to try removing the NFB and/or swapping the OPT primaries tomorrow to see if that fixes it.
As far as the other channel, I think it will behave the same once I get the proper heater winding connected.
I still can't believe the diagram is wrong right from Antek... The orange and brown wires are for a 12.6 volt winding, NOT 6.3 as it says. That means I have only one 6.3V, 4A winding, which probably won't be enough for all the heaters.
I pulled the tubes on the left channel, which did indeed have a 12 volt heater winding connected to it.
I was then able to bring the voltage up on the variac, and got audio through the right channel before it fully warmed up and started oscillating. I'm going to try removing the NFB and/or swapping the OPT primaries tomorrow to see if that fixes it.
As far as the other channel, I think it will behave the same once I get the proper heater winding connected.
I still can't believe the diagram is wrong right from Antek... The orange and brown wires are for a 12.6 volt winding, NOT 6.3 as it says. That means I have only one 6.3V, 4A winding, which probably won't be enough for all the heaters.
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