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I would like to build an amplifier

Kegger said:
There a various ways to design/build amplifiers, many build based on what they have,
be it tubes, chokes, speakers, output transformers or even power tranny's.

Most of my builds are based on what I have laying around that I want to build something
with rather then buy all new things based on what is wanted. :)
Click to expand...

Me too Keg, and that gives me an idea. It might be a good idea for jvdk01, to become a subscriber, and look for a trade up in barter town. Someone may have one a little stouter, and want that one for a pre.:scratch2:
 
Actually, I think I have bigger problems than finding a design. I was looking at resistance readings on the primary side of the OPTs and on one of the OPTs, the red to the blue reads open. The red to the brown is 430 ohms. On the other one, red to blue is 380 ohms and red to brown is 440 ohms. I'm not sure if the resistance numbers are good, but I'm assuming the one that shows open is not. So maybe the solution is to build a mono amp to learn something even though I didn't really have a desire for one, or maybe come up with some other project. This is probably a stupid question, but can you use half of the OPT to make a SE amp. Would this power transformer be suitable some sort of lower powered PP or SE amp if I were to buy different OPTs. By the way, I am a subscriber. I felt guilty before asking for help and not contributing anything, so I became a subscriber a few months ago.

Thanks again
John
 
I have been following that thread, and it actually crossed my mind when I discovered my problem. I think I will go that direction once a BOM is available and then look for some help with the power supply if you don't mind. I guess if I go this route, I'll have to think about speakers. Currently my most efficient pair is 89 db. I suppose it's fun thinking about possibilities.
 
I have powered 89db speakers with 3.5-5watt amps reasonably well to "decent" volume.

In the 6LU8 amp it will pretty much take all your power tranny, a 6MF8 can run in there
and drop off some of that current load, the cathode resistor can be raised for the 6LU8
as well to take off a bit of current to, so it will work with your power tranny.

Or you can still do the 6V6 and the drivers I mentioned for the push pull version by just
going Single Ended, it would cost you $40.00 for your pair of the same outputs as 6LU8
amp used and $20.00 for a pair of the same chokes.

This would run your power tranny at roughly 90ma, so some extra room there and your
heaters currents would have room to spare as well.

Attached is the power supply and a circuit layout for a stereo 6V6 SE, UL amp, 1 signal
channel is shown, just build 2 like that on a chassis and you'd have a nice little amp. :)
 

Attachments

  • 6v6_SE_PS.GIF
    6v6_SE_PS.GIF
    27.1 KB · Views: 115
  • 6V6_300V_SE_UL.GIF
    6V6_300V_SE_UL.GIF
    7.4 KB · Views: 169
jvdk01, post up a picture of the side of the output transformer, showing the numbers stamped into the bell. Maybe someone has one of those laying around?

Regards,
Gordon.
 
GordonW said:
jvdk01, post up a picture of the side of the output transformer, showing the numbers stamped into the bell. Maybe someone has one of those laying around?

Regards,
Gordon.
Click to expand...

Someone painted them sometime in the past, so no number. I took the bells off, and there was nothing inside. I may do what Kegger suggested. I'm not in a hurry. I just wanted a project to learn some things.

Thanks
John
 
Hi

I've been gathering the parts to build this amp, and I have a few questions.

What voltage rating should the capacitors be. My first thought would be something more than 300 V, but I'm not sure.

What rating should the resistors be (1/2 W, more, less).

On the power supply schematic, I'm assuming the lower right hand corner is tied to ground. Is that a good assumption.

I ordered the Edcor transformers you suggested, but they won't be shipped for a month or so. Just so I had something to fool around with, I ordered two of the transformers in the PDF attached below. This is what the seller said: "For single ended 6V6/6BQ5 and 6L6, I'd use 0 and 4 or 8K for primary; or 2 and 8K (as a 6K primary)." I'm not sure how to wire them with this information or if they are even useable. I should have asked this question before I bought them, but it's too late now.

To continue with the theme of asking the question too late, I ordered some 6F6 tubes for cheap as I had read they could be a direct substitute for 6V6 tubes. Can I just substitute them, or should the circuit be tweaked, or should I just toss them out. They are metal as opposed to glass, so I won't even get to see them glow.

Sorry for such basic questions, but I'm pretty clueless.

Thanks
John
 

Attachments

I don't see how those would work at all for a single ended amp. Those line-transformers are designed to have NO DC current through them. They'll saturate almost immediately with the plate current.

NOW... that said, it looks like it MIGHT be a prospect for a very small PP amp. According to my calculations, if you use the 2000 ohm tap as the center tap, the 8000 ohm tap and the primary "ground" tap as the plate leads, and use an 8 ohm speaker on the 4 ohm secondary tap... you wind up with an 8K center tap transformer.

With that, you could go back to the idea that Kegger had earlier... maybe triode mode 6V6s or such. Dunno how the transformer would handle the plate voltage... but it MIGHT work...

If it were me, I'd be looking to use a tube that would work with lower plate voltage... such as a 6EH5 or similar. If you did that, I think you'd just run an 8 ohm speaker to the 8 ohm tap (or 4 ohm to the 4 ohm tap). You could use a 1:1 transformer as the power transformer (it would want around 120 to 150v B+ max), and I'd guess around 5-7 watts per channel in pentode mode...

Regards,
Gordon.


Regards,
Gordon.
 
That's OK about the transformers as paid very little for them, and I have the Edcors on the way. I do plan on building the amp Kegger drew up for me in post 25, but since I have to wait a month or so for the Edcor transformers, I bought the other transformers without thinking. What about the 6F6 tubes. Was that a bad idea also. I haven't bought the capacitors or resisters yet, so I haven't thrown that money away yet. What ratings would be good for those.

Thank you
John
 
It all depends on how much B+ voltage those Speco transformers can handle, before the insulation starts to break down.

If they can handle 250V B+, then the 6F6s could be used, with pretty much the same PP 6V6 triode mode circuit that Kegger initially was talking about. You would have to change the cathode resistor (probably around 25% higher resistance or so), but it might work. As I said- the 8000 ohm (.625watt) tap as one of the plate leads, the 2000 ohm (2.5 watt) tap as the center tap to B+, and the common tap as the other plate lead...

Regards,
Gordon.
 
I've pretty much written off those Speco transformers. I was talking about using the 6F6 tubes in the SE UL schematic Kegger posted (post 25) once the Edcor transformers come in. It sounds like they should be fine, but I wasn't sure. I'm still unsure of the ratings for the caps and resistors.

Thanks
John
 
Alright I calculate the 6F6 should work, they give triode operation in the PDF with a max
plate voltage of 350v so a 300v supply should do here, just tweak the first cap to get it.

Looks like the cathode resistor for the 6F6 should be around 560ohm to get you roughly
37ma (you'll need to measure once you build it)

All resistors I would use 1/2 watt carbon films except the 47k driver plate load should be
2-5 watt carbon film, carbon comp or non inductive wirewound same for the 6F6 cathode,
the 1K to the front end say 1-2 watt whatever type you want to use.

All power supply caps 450v rating or higher, the .22uf cap 250v or higher, on the output
bypass cap 35v or higher, I'd say 50v should be fine.

In the power supply layout I posted the far right is just the simulated "load" of the whole
amp, the bottom line on that is your common/ground the top line will connect the output
tranny and the front end like on the amplifier schematic.
 
Thanks a lot. I wish I could start now, but the Edcor transformers won't ship for about four weeks. I guess that gives me time to draw a good layout.
 
Hi all

I'm resurecting this thread because I finished building my amp today. I think it sounds great, but I am biased. At first it sounded a little thin, but it really sounds wonderful after playing for a few hours. For the plate, I found a piece of scrap and cut it to size with my angle grinder. I painted the plate hammertoned grey and the PT a textured flat black. I made the base from some leftover bamboo flooring. It doesn't look too bad even though nothing's square. I'm listening to music from my computer as I type. I'm a little giddy sitting here thinking about soldering a few bits together, plugging in some tubes and having great music come out. It's like magic. Sorry for the rambling, but I'm pretty happy the way things turned out. Thank you very much Kegger for the schematics and for helping me by helping all the other people who have questions. The same goes for all the people here who share their knowledge so freely. Anyways, I thought I'd share a couple photos.

John


3601865143_b825168c7c_b.jpg


3601865313_c01f74068e_b.jpg


Gratuitous glowing tube. (unfortunately the output tubes are mostly black, so not as impressive)

3602678124_7e5d8f6f0b_b.jpg
 
Very nice work. You might still want to cage those OPTs just in case. Sometimes you can find those wire "in baskets" or similar at the thrift store for that purpose.
 
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