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Old 22nd February 2011, 04:16 PM   #1
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Default I need a project......preferably a HIFI amp..........

I have experience working on and scratch building guitar amps. I would like to stay away from PCBs, I like building my own turret boards or PP wiring. If theres not a basic circuit out the that will get me to the end of the project, I will need some hand holding. Some of the stuff you guys do with HIFI amps I have never seen working on or building guitar amps.....so be gentle. As far as tubes go I've got a stash, 7591, 6550, EL34, 6L6, KT66, 6V6 and standard guit fiddle preamp tubes along with a bag of 6AU6s and 6U8As assorted assorted others.

Maybe 30w + PP using some of the iron I already have. That being:


300-0-300, 250mA
6.3V, 4.8A w/CT
5V,3A w/o CT

Emo0731 same as above but

and a

6.3v, 7A w/o CT
5V, 3A w/o CT

Most of the OPTs I have are for guitar amps. But I do have a:

EDCOR Electronics Corporation. CXPP100-MS-4.2K.

A couple of these;

TF110-48/UL Deluxe Style Ultra-Linear Output Transformer 4/8 ohm (Plastic Bobbin)

And a set of used Iron, PTs and OPTs, out of a Bogen HiFI running 6V6s PP, not UL though. And assorted old pulled stuff.

I am thinking the 6V6s won't realistically get me to 30W. But this is basically what I have in iron. I also don't mind sending some money to add to what I already have.

I listen to Blues, Jazz and Classic rock and will probably end up building some better speakers also.

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Old 22nd February 2011, 04:26 PM   #2
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I used 80W guitar transformers for 40W Hi-fi amps. Work nice. CXPP100-MS-4.2K is a nice beast, but for 6V6s I would not waste it, rather for 4xGU-50 it would be in a ballpack (something like 160-200W of peak power).
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Old 22nd February 2011, 06:06 PM   #3
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If you don't plan to dime the amp and/or don't mind losing some bottom-end at high volume, those guitar amp transformers are an option. Some feedback may get some of that back. Your power requirements put you in Dynaco ST-70 territory, for which there are a plethora of toplogies for (lots of driver board options, which your can wire PtP of course). Any of those output tubes besides the 6V6 will get you there. The primary impedance of the OPT is a bit high, but if you use a 4 ohm speaker on the 8 ohm tap, you get 3300 ohms which might work well for trioded 6550?

If you are willing to buy more iron, the options are nearly endless!
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Old 22nd February 2011, 07:57 PM   #4
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I am not at all opposed to buying more iron. I just wanted you all to know what I had as maybe a starting point. I would like to use the big Edcor OPT, but if not that fine. I think if I were going to use the 25W UL OPTs I would use the 6V6s or the like.

Not familiar with the GU50.

I read some of the EL34 threads with interest, sounds like you'd need a Pentode-PI-EL34 arrangement.

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Old 22nd February 2011, 08:05 PM   #5
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Which OPT are you talking about?

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Old 23rd February 2011, 12:12 AM   #6
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MS = Multiple secondaries? Could be abused to reflect a different primary impedance?
I'm just sayin 4.2K Plate to Plate might not be your only option.
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Old 23rd February 2011, 12:19 AM   #7
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Yep, It has 4,8,16 secondaries. Wieght just under 10 pounds.

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Old 23rd February 2011, 12:29 AM   #8
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If you want that 6V6 similar sound, but more power, there is 6JC5, a 19 Watter, likely want more like a 6.6K P-P primary with them though.
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Old 23rd February 2011, 12:33 AM   #9
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Seems like you're almost there with the 6550's and the 325-50-0-325, 400mA power transformer......fixed bias UL PP 6550?
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Old 23rd February 2011, 12:51 AM   #10
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If I need to and I'm going to buy new 6.6 OPTs, which is not a problem, maybe I should build an El Cheapo Grande as suggested by Mr Eli, w/7591s UL. My problem is that I'm going to need a lot of help drawing up a correct schematic for the power supply with using the 325-50-0-325 400ma PT I have. And the schematic that I have has 12AQ5 power tubes, I may be able to deal with plugging in the 7591s that schematic.

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