ST35 chassis prototype

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ST35 chassis prototype

Postby Uncle Ned » Sat Nov 25, 2006 2:02 pm

This is a sample of the ST35 chassis I am having made. The holes might look a little off circular as this was machined, the production models will be punched. I put a hole over the bias adjustment pots and holes for pin jacks so bias can be set from outside. The output transformer holes are drilled to take the Z565 and Hammond 1650F, there will be holes drilled for a C354 or 156R choke.
The power transformer mounting hole is for an Antek toroid, but because the plate is aluminum, drilling holes to accept the PA774 or Hammond transformers won't be a problem.

The base is quarter-sawn oak, which is nice stuff.

Image
Last edited by Uncle Ned on Sat Nov 25, 2006 3:37 pm, edited 1 time in total.
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Postby sorenj07 » Sat Nov 25, 2006 2:59 pm

sweet, i love quartersawn. is the antek toroid the 360-0-360? i'm using a 275-0-275 in a pi filter for ~305V for my 6P14P amp, i hope it works out ok.
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Postby Uncle Ned » Sat Nov 25, 2006 3:36 pm

sorenj07 wrote:sweet, i love quartersawn. is the antek toroid the 360-0-360? i'm using a 275-0-275 in a pi filter for ~305V for my 6P14P amp, i hope it works out ok.


It's sized for the 275 volt model. You should get more than 305 volts out of that!
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Postby sorenj07 » Sat Nov 25, 2006 7:11 pm

i could, but my input capacitor is only 4.7uF. i needed more than ~250V with choke input, but had to leave a safe margin to not blow the rectifiers with potentially high current draw (i can handle up to 300mA safely)
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Postby TerrySmith » Sat Nov 25, 2006 10:00 pm

I have one of those Antek toroids, 275 - 0 -275 volts. Do you know where I can find a cover or housing suitable for it? Looks like a really good X-former, just kinda ugly!
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Postby sorenj07 » Sat Nov 25, 2006 10:42 pm

yeah it isn't amazingly pretty. 500mA into 550V isn't half bad though, and the two 6.3V 5A filament windings are sweet. If worst comes to worst, you can just stick it inside a bigger chassis, right? Yellow_Light_Colorz_PDT_07
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Postby Uncle Ned » Thu Nov 30, 2006 3:37 am

TerrySmith wrote:I have one of those Antek toroids, 275 - 0 -275 volts. Do you know where I can find a cover or housing suitable for it? Looks like a really good X-former, just kinda ugly!


On the chassis above, the power xfmr goes inside the chassis, so no cover is necessary.
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Re: ST35 chassis prototype

Postby Shannon Parks » Thu Nov 30, 2006 6:30 am

Uncle Ned wrote:The power transformer mounting hole is for an Antek toroid, but because the plate is aluminum, drilling holes to accept the PA774 or Hammond transformers won't be a problem.


Cool to see the Antek getting used. BTW, Hammond 1650Fs and Z565 can fit into the same footprint I believe. I squeezed my 1650F into that Soundtastick footprint without trouble.
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Postby mesherm » Fri Dec 01, 2006 6:10 pm

Ned, what are the dimensions of that chassis. I have a Soundtastik chassis already for my DIY35 but I have another amp project that need one.
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ST 35 Chassis

Postby leadtower » Sun Dec 03, 2006 6:33 pm

Thats a beaut; Will there be a for sale edition some day? Also a nice pair of holes for two mono volume pots and an on/off switch in the front would be real nice. Another thing I personally would like to see is an output strip cutout in the rear for both 4 and 8 ohm speaker jacks. and last; handles; maybe nice small brass side bars or top bars. I always find it easier to pick the amps up from inside the shelving if there are some handles to grip.
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Re: ST 35 Chassis

Postby Uncle Ned » Tue Dec 05, 2006 8:10 pm

leadtower wrote:Thats a beaut; Will there be a for sale edition some day? Also a nice pair of holes for two mono volume pots and an on/off switch in the front would be real nice. Another thing I personally would like to see is an output strip cutout in the rear for both 4 and 8 ohm speaker jacks. and last; handles; maybe nice small brass side bars or top bars. I always find it easier to pick the amps up from inside the shelving if there are some handles to grip.


I didn't take a picture of the back , but there's a plate back there for input jacks, binding posts, etc. I don't think I'll put a hole in the front, it just looks messy if someone doesn't want a volume control, that can go on the back if the user wants one. Other issue is I'm trying to minimize the amount of woodworking, which is expensive.

I don't think top handles are a good idea as the plate is only held in place by wood screws.

This example top plate has a few boo-boos, but the shop is working on a corrected version, I'm supposed to have a sample this week.

Best Regards, Ned
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Postby Uncle Ned » Tue Dec 05, 2006 8:14 pm

mesherm wrote:Ned, what are the dimensions of that chassis. I have a Soundtastik chassis already for my DIY35 but I have another amp project that need one.


The plate is 12 X 12 inches, the base is 3 inches deep. There's enough room under there for a choke and Antek xfmr, if you want to use a conventional transformer there's room to put a rectifier tube on top, too.
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Postby Ty_Bower » Thu Apr 05, 2007 7:44 am

TerrySmith wrote:I have one of those Antek toroids, 275 - 0 -275 volts.

Where are people finding these Antek 275-0-275 toroids? All I seem to be able to locate are the 500CT and 600CT models on eBay.
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Postby Uncle Ned » Thu Apr 05, 2007 9:31 am

Ty_Bower wrote:Where are people finding these Antek 275-0-275 toroids? All I seem to be able to locate are the 500CT and 600CT models on eBay.


Apparently they discontinued the 550VCT one. The 500V and 600V ones fit on this chassis.
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An-Tek Toroids: 325VAC version probably best for ST35s

Postby EWBrown » Wed Oct 17, 2007 9:10 am

I recently completed the ST35 on the "Tube Zone" base, using one of the 300VAC An-Tek toriods.

I had some minor "issues" getting the bias set to 35 mA, which turned out to be that the B+ voltage was around 345VDC, instead of the expected 365 to 370 VDC. These toriods have a "true" 115V rated primary, , so they will have less "300VAC" on the secondaries, than will the Hammond 272FX, which runs on the high voltage side.

I could get J/J tubes to 35 mA, but some NOS RCA's, and Russian 6P14Ps topped out around 32 mA, max.. I had to set the RK to about 350 ohms (the minimum was 345 ohms, with 510 ohm resistors) to get 35 mA out of the JJ/s, where 400 ohms is pretty much "normal" for these tubes with a more "normal" 365VDC B+.

I corrected it by lowering the "main" cathode resistors back down from 510 ohms to 470 ohms, and everything runs and sounds great! (I think this was the original Rev B and C board spec'e value).

I'd suggest using the 325 VAC version of this trannie, in order to get the correct B+voltage around 365-370VDC, at the OPT CTs.

Anyhoo, these An-Tek toroids do run at a lower temperature than do the PA774s and 272FXs, and they seem to have plenty pf power reserve, even at the somewhat lower B+ voltage, thanks to a fairly hefty current rating.

The slightly low B+ seems to have a different, and I'd say a "smoother" sound quality, perhaps the sacrifice of a couple of watts might be a good trade off... That's something which really needs instrumentation to analyze, rather than my less than perfect ears Yellow_Light_Colorz_PDT_06

FWIW, An-Tek has their own website, separate from e-bay, and the unit prices are a bit lower, as well. www.toroid-transformer.com

/ed B in NH
Last edited by EWBrown on Wed Oct 17, 2007 12:30 pm, edited 2 times in total.
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