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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 28 Mar 2020, 11:29 
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Suncalc wrote:
The peak clean power output is 1.3 watts RMS per channel...

I still can't get over how good and how loud this amp sounds. It handles everything from classical, to blues, to choral music equally well. And the sound stage is awesome. I will never go back to building common power supply filters for both channels ever again.


I am brand new to this forum and tube amps. I have always loved the sound of tube amps whenever I heard them, and I absolutely love the glow factor and your amp looks amazing.

I apologize if this is a stupid or newb question, but I am wondering what size drivers 1.3 watts is capable of driving. I realize most amplifier wattage claims are grossly inflated, but just curious what this amp can drive well speaker wise?

I am looking to make my own speakers as well, and am considering these full-range 8" drivers. Just wondering if this amp would be powerful enough to drive them and how loud they could get (I am NOT looking to go super loud)?


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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 28 Mar 2020, 11:42 
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Joined: 28 Mar 2020, 11:16
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Suncalc wrote:
The peak clean power output is 1.3 watts RMS per channel

I still can't get over how good and how loud this amp sounds. It handles everything from classical, to blues, to choral music equally well. And the sound stage is awesome.


I hope this isn't a second reply... it looks like my first reply disappeared without actually posting. I'm brand new to this site, so not sure if I am doing things right.

What I was trying to ask was what kind/size speakers could this amp drive? I am brand new to tube amps, though have always loved how they sound. I also know that many newer amps have exaggerated listed power ratings.

I would love to build this amp and a set of speakers for casual listening (meaning, not extremely loud), but I am wondering if 1.3 watts is enough. I would like to use these 8" full-range drivers. Their sensitivity is 95dB at 1W/1m. I'm not trying to fill a large room with loud music, so wondering if I could get by with this?


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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 01 Apr 2020, 17:05 
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Joined: 03 Jul 2019, 10:36
Posts: 7
Hi BabblingBafoon, should be OK with those drivers. Elsewhere in this thread people recommend fullrange drivers in the mid nineties. Sounds like you're thinking same as myself, using efficient speakers to match with the 6CY7 Stereo Amp. I opted for the Fane 12-250 tc driver, at 100dB/Watt it's efficient, but needs a good sized box. Speaker's practically finished, but the guts of an amp are still in a cardboard box upstairs.


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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 01 Apr 2020, 18:36 
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Joined: 06 Apr 2009, 10:08
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Location: US Pacific Northwest
BabblingBafoon wrote:
I would love to build this amp and a set of speakers for casual listening (meaning, not extremely loud), but I am wondering if 1.3 watts is enough. I would like to use these 8" full-range drivers. Their sensitivity is 95dB at 1W/1m. I'm not trying to fill a large room with loud music, so wondering if I could get by with this?
You should be just fine under those conditions.

On those drivers, 1.3w per channel stereo is 108dB + 3dB at one meter. This is a lot of volume in a small to moderate sized room. My office, where I regularly use my 6CY7 amp, is about 11' x 12' (3.35m x 3.66m) and I have never had it up to full volume in that space. Normally it is run with the volume between 10 and 12 o'clock. This amp will never make the windows shake, but it will provide some very fine music at moderate listening levels.

It is actually amazing how much consumer electronics have been produced with less than 1W amplifiers. I think you'll be fine.

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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 02 Apr 2020, 07:33 
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Joined: 28 Mar 2020, 11:16
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I believe the room I would use this in is even smaller than that, so sounds like it would be perfect for me. Thanks for the quick reply!

Now I have to read through your project page more closely and see if I can figure out how to build this bad boy! LOL You don’t, by any chance, build to sell, do you?


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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 20 Jun 2020, 18:20 
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Location: US Pacific Northwest
This amp first debuted in May of 2015. At that time I wanted to convert a design that had been gathering dust in my projects folder into a real amplifier. And, I just happened to have a suitable chassis available that wasn't being used. Since then, I have had several questions from various people about using the Edcor GXSE transformers for maybe a little bit better low end response.

Well, I have finally revisited the design and have made some modifications which make the schematic better suited to the GXSEs and which I think should yield some interesting results. Here is the modified schematic:
Attachment:
Schematic_V2.jpg

In addition to the output transformer change, I have increased the cathode bypass on the power stage (to support better low end response) and increased the interstage coupling capacitance (also to support low end response).

When I first designed this circuit, I was playing with some budget output transformers that get very mushy at the low end. Some of my design decisions at that time were compromises for those output transformers; and they persisted in the original schematic. I have also changed up the power supply a little bit for better channel separation. And finally, I chose to use an Edcor power transformer for this build as it stays much cooler than the Hammond. I wanted this characteristic because the transformers will be in a wood alcove and I didn't want to thermally stress the wood any more than necessary. Additionally, the added filament winding capacity will allow me to use a jeweled indicator on the front of the amp.

And just so people don't think this is merely an academic exercise, here is the chassis in dry fit, sitting on my workbench.
Attachment:
V2_Dry_Fit.jpg

When I get a little further on with the project I'll post an update. I intend to give this amp a full set of testing for frequency response and distortion. I am shooting for marginally better performance than the original and better channel to channel separation performance.


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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 24 Jun 2020, 17:32 
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Joined: 03 Jul 2019, 10:36
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Nice choice of wood for the cabinet, it should look spectacular when it's finished, is it tiger wood?
I'm looking forward to hearing how the new schematic works out because already bought the iron for the original 6cy7 amp.
Instead of XSEs I've got GXSE Edcors for output in the otherwise original schematic,for the moment though, I'll hold off doing anything more until I hear about the new design sounds.


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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 24 Jun 2020, 20:52 
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Location: US Pacific Northwest
soundoutlad wrote:
... is it tiger wood?
Nope. Actually it's Zebra Wood {Microberlinia brazzavillensis}. I'm planning on several coats of oil to really bring out the grain and color. I just got finished fitting all the metal and have started the final sanding of the chassis.

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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 28 Jun 2020, 12:37 
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All the metal pieces have been test fit and are ready for paint. And the Zebrawood chassis is complete, has been hand sanded to 600 grit, and is ready for its oil finish.
Attachment:
Metal_Fit.jpg

Attachment:
Sanded_1.jpg

Now comes the long careful process of several coats of oil finish on the chassis and primer and paint on the exposed metal pieces.

This new amplifier is taking shape.


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It's all about the Glass!
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 Post subject: Re: 6CY7 Stereo Amp
PostPosted: 28 Jun 2020, 17:37 
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Joined: 06 Apr 2009, 10:08
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Location: US Pacific Northwest
First coat of oil is on the chassis. What do people think?
Attachment:
Oil_1st_coat.jpg


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