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Old 12th July 2007, 06:40 PM   #1
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Default Hammond 1650F

Any experience with this opt? I'm thinking about a MKIII or ST35, as I have two 1650F's.

What about power xfrmr? I have been hearing that the 270/272/370/372HX series wil work ok, which one is the best?
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Old 12th July 2007, 11:17 PM   #2
Sherman is offline Sherman  United States
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No personal experience with the 1650F but it has a primary Z of 7.6K while the MK III trafos were 4.3K. It is also rated for 25W while a MK III is a 60W amp.

So... it would be better suited to an ST35 with EL84 power tubes. Both the impedance and the power rating are well matched to the 15W or so the ST35 makes. You might also consider Uncle Ned's ST35 "kit" based on DIYTUBE PCBs. Should be a good match.

The 270HX would supply enough current and voltage, lower models in the 270 series would be light on current depending on your biasing.

The 3xx series have a larger core and are beefier all around than the 2xx series PTXs. I've used several 2xx series and all had some degree of mechanical buzz which I mitigated by mounting on rubber washers. The 3xx series reportedly are much quieter mechanically and less "on the edge" at their rated output.

HTH,
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Old 12th July 2007, 11:20 PM   #3
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Default Re: Hammond 1650F

Quote:
Originally posted by ThSpeakerDude88
Any experience with this opt? I'm thinking about a MKIII or ST35, as I have two 1650F's.

What about power xfrmr? I have been hearing that the 270/272/370/372HX series wil work ok, which one is the best?

The ST35 circuit and "El Cheapo" should be OK with the 1650Fs. Forget about KT88s, as the end to end impedance is too high and the power handling capability is too low.

IMO, it's HARD to better the price/performance of a properly executed voltage doubler B+ supply. Revered designs, including the H/K Cit. 2, Marantz 8B, and Fisher 500C, use doubler PSUs.
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Old 13th July 2007, 04:52 AM   #4
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sorry, I didnt mean mkIII, I was thinking of this schematic http://www.ampslab.com/SCHEMATICS/Dynaco6BQ5.gif.


El-Cheapo looks like a nice circuit to breadboard , I may try a mono to see what I thinkbefore building. Also, I have a 270FX. I know it is rated at 150ma, but with solid state rectification and no use of the 5v tap, would my current capability be better? If its not even worth messing with , I will order a 370HX. However, its what I have for now.
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Old 13th July 2007, 11:26 PM   #5
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Quote:
Originally posted by ThSpeakerDude88
sorry, I didnt mean mkIII, I was thinking of this schematic http://www.ampslab.com/SCHEMATICS/Dynaco6BQ5.gif.


El-Cheapo looks like a nice circuit to breadboard , I may try a mono to see what I thinkbefore building. Also, I have a 270FX. I know it is rated at 150ma, but with solid state rectification and no use of the 5v tap, would my current capability be better? If its not even worth messing with , I will order a 370HX. However, its what I have for now.

With the 5 V. winding inactive, you should be OK with the 270FX. At "idle", El Cheapo draws approx. 132 mA. CLC fiiltration of the B+ using the minimum amount of capacitance in the 1st position necessary to keep the rail voltage up allows you to squeeze a few extra mA. out of the rectifier winding. A Hammond 159S looks OK as the B+ PSU choke.

BTW, tube rectification is OK. A 6BY5 dual damper will get the job done nicely. The 5 A. rating of the 6.3 V. winding is not stressed. 4X 6AQ5s or 6V6s draw 1.8 A. of heater current. A 6BY5 draws 1.6 A. 2X 12AT7s draw 0.6 A. The total heater draw is a comfortable 4.0 A. Don't directly ground the 6.3 V. winding's CT. Grounding via a large 'lytic is OK.

You can use the B- supply shown in the "El Cheapo" schematic. Use a 6AL5 for the vacuum half of the bridge and power its heater from the B- power trafo.
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Old 14th July 2007, 12:27 AM   #6
dmason is offline dmason  United States
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I have a pair in a Class A PP triode 6EM7. They are surprisingly musical, with good low end grunt. Outstanding value IMO. Hope this helps abit...
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Old 16th July 2007, 06:06 PM   #7
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I have the other 1650F on the way. I found a comparison to the original dynaco opt's and the hammonds are close and great for the price.

About the power x-frmr: Can I use SS FWB ? I thought that if you did that, instad of using the x-frmr centertap, that you could dish out more current because you weren't passing DC through the x-frmr windings.
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Old 16th July 2007, 11:26 PM   #8
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Quote:
Originally posted by ThSpeakerDude88
I have the other 1650F on the way. I found a comparison to the original dynaco opt's and the hammonds are close and great for the price.

About the power x-frmr: Can I use SS FWB ? I thought that if you did that, instad of using the x-frmr centertap, that you could dish out more current because you weren't passing DC through the x-frmr windings.

Dude,

If you bridge rectify the end to end voltage of the rectifier winding, you get twice the V. and half the A. Surprise (NOT), TANSTAAFL applies. The rectifier winding has a fixed VA rating. Also, there is no "standing" DC, when the "classic" FWCT circuit is employed.
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Old 17th July 2007, 04:01 AM   #9
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I meant the B+ winding, not the rectifier winding.


Please explain more about FWCT? I was told that each half swings +/- from ground point and is rectified, and that DC flows through the ct. Maybe I am tired and confused...

Now I know that with a standard non CT transformer if you bridge rectify you get ~1.414*Vac , and .707* I.
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Old 6th August 2007, 03:21 AM   #10
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well, they have the 272/270hx, and the 300 series versions. The HX series are rated for 200ma. The other option, is a 302AX. It is rated at 200 ma also.. and I don't exactly see much difference between it and the 370 HX.


Here are my main questions: How much current does a typical 15-20 watt/ch stereo 6bq5 amp need ( with safe headroom to prevent overheating the xfrmr)

What voltage should I choose... 275v or 300v. 275v will be easier on the tubes wont it? Also, there is a huge price difference between the 200 and 300 series.

a 270HX is $62, while the 370HX is $93. Is it really worth the extra bucks, with enough current on tap ( assuming I am running 120v into a 117v xfrmr for the 200 series.)

the extra money could go into some good coupling caps if I went the 200 route... what do you guys think?
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