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Old 28th June 2011, 11:46 PM   #391
AJT is offline AJT  Philippines
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Quote:
Designed in USA Made in China
in the early 70's that would have bee: "Designed in USA Made in JAPAN by Tamura Radio"

and then later, "Designed in USA Made in South Korea"

and still much later, "Designed in USA Made in Taiwan"

off-shore operations made your US based companies much more competitive....
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Old 29th June 2011, 03:19 AM   #392
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Tonight I tried a alternate equivalent output tube from the former Soviet Union.

So I now have two options for the output tubes, and both take the abuse.

I've cranked them up to 330V B+ and got over 3W into 4 ohms at 1KHz.

When I pushed it to 13Vp-p square wave out into 4 ohms, it failed to elicit red plates after 20 minutes so I gave up. I did increase the cathode resistors to 220Ohms to limit the cathode current to 25mA and plate current to 2X rating. (I guess it is a tad less plate dissipation since that includes the screen current in with the plate current, bad math.)

I like these tubes.
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Old 29th June 2011, 01:05 PM   #393
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Not to throw a monkey into the wrench, but for the output tube could we use a buck 6n6p in pp with a 4k load? That should be good for 2watt at least.

http://www.pastisch.se/faktiskt/amp86.gif
http://www.pastisch.se/faktiskt/amp87.gif
http://www.pastisch.se/faktiskt/6n6p_6h30.jpg
http://www.pastisch.se/faktiskt/a_qrps.gif
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Old 29th June 2011, 01:20 PM   #394
TheGimp is offline TheGimp  United States
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Since the only restriction is availability, I would think you could. You might want to test with the JJ ECC99 or a set of 12BH7s if you can find them. Wiring for optional 6V /12V would make the 12BH7 an option.

6FQ7 might work as well, althought he 12BYH7 and 6FQ7 have lower plate ratings.

Last edited by TheGimp; 29th June 2011 at 01:26 PM.
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Old 29th June 2011, 05:48 PM   #395
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I definitely need to try it with better speaker... Good overdrive, without any additional diode screen grid itself creates significant sagging and compression.
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Old 1st July 2011, 10:01 PM   #396
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OK, well, I've been thinking about building a guitar amp for probably 20 years, much more seriously for the last 5 years since my son plays. This thread got me going to sort through some of my very old parts. I have a real lot of "junk" for a person who is not that into tubes. A friend gave me an old Realistic integrated stereo tube amp for "parts" many years ago. I told him several times I did not want it, LOL, but he insisted. It had 6BM8 outputs, and was a rather odd design so I gutted it to use for some tube preamp experiments and it has been sitting ever since. Today, it would probably go for $200-$300 at that site but who would have known back then!

I'm going to use this to do some prototyping and I had planned, years ago, to do something with a small 20-40W power amp for testing. I have a good number of octals, 5881, 6L6GTs so I cut the chassis to take octal sockets for the outputs. Rebuilt the power supply and am getting +380V no load, 340 at 100mA with 5881s in the outputs.

I'll probably use some 6V6 type tubes for 10-15W if I decide to enter this contest. I've got a pair of old 6V6s where the glass is black all the way around, why was this done? One is a Raytheon/Germany 6V6 GTA and the other is a Kenrad 6V6GT, don't remember where I got these. I also have a nice old pair of Amperex 7408s that match up pretty well.
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Old 1st July 2011, 10:13 PM   #397
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Originally Posted by PB2 View Post
OK, well, I've been thinking about building a guitar amp for probably 20 years, much more seriously for the last 5 years since my son plays. This thread got me going to sort through some of my very old parts. I have a real lot of "junk" for a person who is not that into tubes. A friend gave me an old Realistic integrated stereo tube amp for "parts" many years ago. I told him several times I did not want it, LOL, but he insisted. It had 6BM8 outputs, and was a rather odd design so I gutted it to use for some tube preamp experiments and it has been sitting ever since. Today, it would probably go for $200-$300 at that site but who would have known back then!

I'm going to use this to do some prototyping and I had planned, years ago, to do something with a small 20-40W power amp for testing. I have a good number of octals, 5881, 6L6GTs so I cut the chassis to take octal sockets for the outputs. Rebuilt the power supply and am getting +380V no load, 340 at 100mA with 5881s in the outputs.

I'll probably use some 6V6 type tubes for 10-15W if I decide to enter this contest. I've got a pair of old 6V6s where the glass is black all the way around, why was this done? One is a Raytheon/Germany 6V6 GTA and the other is a Kenrad 6V6GT, don't remember where I got these. I also have a nice old pair of Amperex 7408s that match up pretty well.
Doubt if you would get a design with 6V6's that would come in for under a hundred bucks. The whole idea was to come up with a design that more or less anyone can build under that amount. Mind you with the price of cheap amps on the market it is only us real diehards that would bother.
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Old 1st July 2011, 10:47 PM   #398
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Originally Posted by PB2 View Post
OK, well, I've been thinking about building a guitar amp for probably 20 years, much more seriously for the last 5 years since my son plays. This thread got me going to sort through some of my very old parts.....
It's fun to build things from parts you already have. But the contest requires you use parts that are available from current suppliers that add up to no more than $100. I think surplus vendors are specifically excluded. You have to use NEW parts.

a 6V6 powered push pull amp will be hard to build for $100 because your budget would be mostly consumed by the two transformers. Nothing left for the other parts.

But do go ahead and try it. Build with what you have and tweak it until the sound is "right". Or better yet buy your own guitar and in 8 weeks you'll be playing simple tunes.
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Old 1st July 2011, 11:45 PM   #399
PB2 is offline PB2  United States
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I have a PP design using similar but low cost tubes in a spreadsheet that is coming in at $90 with just about everything covered as outlined for the contest. I used parts that do not have issues with aging from Apex Jr such as pots, line cord, etc. The rest are from normal suppliers.

I'm aware that it has to be built from new parts, this is the prototype, and it will probably morph into something much more complex to test out our Soldano variant.

I asked if Apex Jr. was acceptable and got no response, also asked if 10-15W was - also no response. So if it turns out not to be, then I will not enter.

Anyone know what's up with these black glass 6V6s?
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Last edited by PB2; 1st July 2011 at 11:50 PM.
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Old 2nd July 2011, 12:08 AM   #400
ChrisA is offline ChrisA  United States
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Originally Posted by PB2 View Post
I have a PP design using similar but low cost tubes in a spreadsheet that is coming in at $90 with just about everything covered as outlined for the contest. I used parts that do not have issues with aging from Apex Jr such as pots, line cord, etc. The rest are from normal suppliers.
I kind of lost interest in building a $100 amp head when I found that the Kostom 5H sells for $99, shipping included. You can buy a 5H fromGuitar Center, Music123, Amazon.com any of several others. I'm headed out to the local music store right now to buy some odds and ends, I'll look at a H5 close up when I get there.

For $149 the Fender Champ 600 is a combo in a vinyl covered wood cabinet that sounds as you'd expect with a name like "Fender Champ".

Building it yourself for $100 would not catch many people's attention with retail prices so low. $50 would be truly impressive as would be a combo in a wood cabinet for $100

I don't think using Apex is cheating but the winner is determined by votes so you need to look good to the voters and Apex may not help.
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