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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 17 Jan 2018, 13:55 
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Joined: 23 May 2016, 19:39
Posts: 12
Hello! I am reviewing parts for this project and I was hoping someone could verify if this IEC module with a 1.25A fuse would be appropriate for the Poddwatt?

I haven't used one before and am unsure if it would be appropriate for this build.


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PostPosted: 18 Jan 2018, 11:06 
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Joined: 23 May 2016, 19:39
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Posting again - I found this type for way cheap and just had to snag a couple just in case they work.

Could someone please tell me if the ones from jameco are good for this project?
LINK TO IEC MODULE I DID BUY


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PostPosted: 18 Jan 2018, 11:19 
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Joined: 16 Feb 2016, 19:45
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Location: Boston, USA
Someone else may comment, but I would expect that any of these power entry modules would be fine. I used a cheap one and the biggest problem was cutting the hole for it in the Hammond chassis I used! Be sure you read all Bruce has to say on grounding before you wire up your project, that is critical to good performance.

I love my Poddwatt; I use it every day at work to listen to tunes. If I were to build another I would not mount the driver tubes next to the power transformer. Not sure I can hear any hum from this but probably not ideal.

Image

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PostPosted: 18 Jan 2018, 21:57 
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Joined: 04 Jun 2008, 20:59
Posts: 3748
Location: Arizona, USA
Hi, Pretty much any IEC entry/power filter will be fine. I use a 2 amp fuse though. My experience with tube gear is that if there is a failure it will usually be large and will easily take out a fuse of that size. I like to have the larger size so as to prevent it from failing due to the turn on surge.

Yes I would not put the drivers close to the power trannie. It is likely to add noise, it may below usual listening levels , but it will be there.

I used a Poddwatt in my office (when I worked for a company other than my own) for over 7 years. It is still in fine shape. The tubes are the originals as well. My main system now uses a pair of the mini-blocks. They are essentially two halves of a Poddwatt Dual Mono Block.

Good listening
Bruce

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PostPosted: 19 Jan 2018, 16:18 
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Joined: 23 May 2016, 19:39
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Thank you! The both of you! It seems I had joined this forum a couple years back when I was first researching tube amps for a record player with a built in preamp but at the time I was too inexperienced to take it on - also I didn't own a record player. I am very excited to work on this. I'll be laying everything out while I wait on the transformer set. The goal is to have it finished once they arrive. So I'll be back in a couple of months to share my project 8-)

Great work, Bruce. Your documentation helps the builder feel very comfortable taking on such a project.

-KM


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PostPosted: 19 Jan 2018, 18:00 
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Joined: 17 Jan 2018, 16:13
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Hi Bruce,

I'm preparing to build Poddwatt EL84 amplifier in a single power transformer. I'm from Poland and cost of Edcor trafos with shipping from US is quite high, so I'm going to order it locally (tailor made ones). I have some quesstions:
1) how strict is anode voltage of power trafo and what is acceptable range (180V to...)?
2) output trafos - UL I guess should be at 43%. What should be input impedance and suggested minimal frequency response range?
3) in the bridge for anode power you have only two diodes, but in many comparable schematics I saw four. What is the difference?

Thanks in advance for the answer :)


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PostPosted: 20 Jan 2018, 16:38 
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Joined: 17 Jan 2018, 16:13
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Hi again,
sorry for repeating questions already answered upper in this thread.
So please ignore my above post and hopefully I will post some pics when the amp is finished :)


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PostPosted: 20 Jan 2018, 21:07 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, You can fudge on the B+ a bit. The problem is the dissipation limits of the tubes. At 250V B+ with 42 ma they are close to max. Dropping to 225 helps a bit, and 200 is actually OK.

With a solid state power supply (as in the design) you can get nearly 1.4 times the transformers RMS voltage for the B+.. 180 VRMS works out to about 252 volts DC.

I use 43% for the UL windings, but really anything from about 35 to 45 is fine.

If you have a single ended power transformer winding (0-180) then a 4 diode bridge rectifier is needed. If you have an 180-0-180 one then the center tap is grounded and only two rectifiers (one on each of the 180 parts of the winding) is needed. The end result in either case is the same.

Good listening
Bruce

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PostPosted: 20 Jan 2018, 22:22 
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Joined: 06 Apr 2009, 10:08
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Location: US Pacific Northwest
gofar99 wrote:
If you have a single ended power transformer winding (0-180) then a 4 diode bridge rectifier is needed. If you have an 180-0-180 one then the center tap is grounded and only two rectifiers (one on each of the 180 parts of the winding) is needed.
I would add one note. If you use a 4 diode bridge on a single winding with a capacitor input filter, you can only draw about 62% of the rated secondary current. If you use a center taped secondary with a complementary 2 diode rectifier, then you can draw the full rated secondary current.

Size your power transformer appropriately.

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PostPosted: 21 Jan 2018, 00:10 
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Joined: 23 May 2016, 19:39
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Any suggestions for including the Groovewatt circuit in the same chassis as the PoddWatt? Could the Poddwatt PT handle the current needed for the 5 preamp tubes?


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