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Old 6th September 2011, 02:24 AM   #1021
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Here is the Eagle schematic that I used to design the PC board for AMP1.2. I will post the complete BOM once I have time to finish tweaking it out. The only mod so far is a 47 uF cap from pin 4 of U4 to ground to kill a background buzz from the series heater string.

Anyone can build this using a more conventional power supply and PTP wiring. Use a 6AU6 for the first tube, a 6AV6 for the second tube and 6AQ5's for the output. That's where I started before optimizing for cost.
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File Type: pdf Schematic.pdf (17.0 KB, 200 views)
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Old 6th September 2011, 02:26 AM   #1022
Cassiel is offline Cassiel  Libya
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Wouldn't it be funny if tubekit wins the challenge? LOL. Once I got lost in a forest, after many miles of walking I ended up right where I started. That was funny too. It was dark and I was tripping but that's no excuse.
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Old 6th September 2011, 02:30 AM   #1023
Cassiel is offline Cassiel  Libya
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Quote:
Use a 6AU6 for the first tube,

I like that.

Quote:
and 6AQ5's for the output.
I like that too.
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Old 6th September 2011, 02:50 AM   #1024
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Quote:
Wouldn't it be funny if tubekit wins the challenge?
Actually it turns out that the lash up I made using 9DX tubes was very similar to Tubekit's design. I didn't like it because it didn't scream. Well not every builder wants a screamer, so it's possible that a mellow design could be preferred over a full metal racket screamer.
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Old 6th September 2011, 02:59 PM   #1025
tubekit is offline tubekit  United States
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Mellow? I'm sure there must be some "mellow" designs out there somewhere.

What I don't quite understand is using the word "mellow" in the same post with the words "Tubekit's design."

I'm quite sure that's the wrong word in this case.

Put a 6LY8 into the socket and it screams. Did someone mention acoustic "feedback"? As in some number of inches between guitar strings and speaker? Change inches to feet for what we're talking about here. Can you say "sizzling"?

There are more than five different options listed in the 73 RCA .

I tried four of them.

I only heard "mellow" once.

The 6LF8 is "mellow." Good for Jazz rhythm and Funk.

The 6KV8 is pretty crunchy, but it can't touch the 6EB8.

Haven't tried the 6KR8 yet.
Or the 6LQ8.
Or the 6JV8.
I'm fairly sure there are others.

I have reason to believe that the 6EB8 is the right one for general use.

Not being as stupid as I've been made out to be, and all.

It looks like there's just no way around it. It's going to take a MOTU and a Shure SM57 to evaporate all these ephemeral pipe dreams and replace them with some substance.

Some people just can't hear the sheet music.
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Old 6th September 2011, 06:42 PM   #1026
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Quote:
What I don't quite understand is using the word "mellow" in the same post with the words "Tubekit's design."
OK, I will admit that I might have used the wrong word late last night. I was trying to state that both designs have practical uses and audiences. So far most of the time I have spent playing with my own amp has been with everything maxed out and wishing it would go to 11.

As I stated before I have no experience with the actual Tubekit design. I threw together a quick lashup of an SE amp using the 9DX base and ran several tubes through it. The schematic was similar to what you posted. I can state that it did sound quite nice and could go well into the distortion zone with some tubes. Choice of OPT and speaker makes a big difference too.

Quote:
There are more than five different options listed in the 73 RCA
There are more than 20 pin compatible tubes that can fit the 9DX socket. I have several samples of most of them and have tried most in several designs. No guarantee that they can all work in your design. They are:

6AU8 6AW8 6BA8 6BH8 6CX8 6EB8 6GN8 6HF8 6HZ8 6JA8 6JE8 6JL8 6JT8 6JV8 6KR8 6KT8 6KS8 6KV8 6LB8 6LF8 6LQ8 6LY8 6MV8 and a few more with odd heater voltages.

The design that I tried was not what I was looking for and I chose not to go further down that road. I have already ditched several other designs too, including the original version of AMP1.2 . As I stated I tend to prefer something that can do clean and transition all the way to full metal racket. With my little speaker 2 watts isn't loud enough either. Other builders might and probably do have different preferences. Eventually we will both get sound clips posted and then we can really hear them. Until then it is all speculation that gets zapped by the moderators.

The 4 tube design that I posted last night does go well into the distortion zone in a good kind of way, but it is still not the ultimate design that I am looking for. The 5 tube design that cranks out about 20 watts and requires all of the $100 budget does get there, but it is more complicated than both of these budget amps combined. I am still working on exactly the right sound but it won't be a $100 amp either.
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Old 7th September 2011, 07:00 AM   #1027
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Default Speaking of tube specs . . .

I expected there would be more tubes that would fit the 9DX socket, but that's quite an impressive list!

I haven't verified all of them but I do have the 6KT8 and it seems I remember a reason for leaving it off of my list and never putting it in the socket. Ah yes, according to the handy old 73 RCA it's not a 9DX tube. Pin 5 is heater, yes, but also g3 and internal shield. Not compatible with the AC filament in this design, but I do have some designs using a DC filament that should work with that side of the filament grounded. Hmmm. Maybe the rest of that list could stand a little review and verification, too.

I'm working on a four-tube 3.5 watt design that goes from sweet and clean to full metal fuzz with a broader frequency response than this one, and includes bass, mid, treble, and spring reverb for the $99 target. It would already be prototyped except that I'm also trying to squeeze a tube compressor into the design without adding any more tube sockets.

Just finished building a test jig with a front face full of milliammeters, multi-position switches and pots, plus two or three separate pairs of binding posts for voltmeters and ohmmeters. I've got this interesting tube for which the published specs don't even begin to tell the story about what happens to plate current when its various electrodes are subjected to the permutations of possibility. I plan to find out. So I'm making spreadsheets, recording the voltage and current in various places.

Making spreadsheets is boring. Very, very boring. But the secret hidden within this tube has begun to reveal itself to me. And that, my friends, is exciting. Very, very exciting! (You've all heard of negative resistance, right?)

From spreadsheets to graphs. From graphs to designs. From designs to the above stated goal. It's all top secret right now, but I'll keep you posted.

Incidentaly, the amp built from the circuits I submitted above puts out over 1.5 watts RMS into an 8-Ohm speaker as measured using a guitar single coil pickup as input.
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Old 7th September 2011, 01:31 PM   #1028
TheGimp is online now TheGimp  United States
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The 6LF8 and 6LY8 looked like some of the best cantidates in the 9DX pin out and I have both but have not tried them since I only had time to finish working with the 6DX8 design (9HX pin out).

9AE is another pinout that looks promising, at least for preamp/driver tubes but I havn't found any tubes in that pinout that will reach a 2W output level.

6GV8 looks good for power but in a somewhat rare pinout, 9LY.

The only spreadsheet I've done was broken down by pinout and different sheets by power level. I probably have a quarter of the tubes in it that George listed.

More confusing is why are 9DC and 9AE the same pin out? Are there others like them where two designations are used for the same pin out?
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Old 7th September 2011, 01:55 PM   #1029
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Quote:
it's not a 9DX tube. Pin 5 is heater, yes, but also g3 and internal shield. Not compatible with the AC filament in this design
I stuffed it into the amp any way since I have pin 5 at AC ground but elevated to about 30 volts DC. I don't remember the details on which tube worked the best in that design.

Quote:
Ah yes, according to the handy old 73 RCA it's not a 9DX tube.
I still have the 1973 RCA tube manual that I bought new at a Lafayette Radio Electronics store in 1973. It still has the $1.25 price sticker on it. It has seen better days. You can download a PDF of the 1975 edition here:

Tube Data

Pete is a forum member here and has scanned more vacuum tube related books to PDF than anyone can possibly read. They are all on his web site to download.

Quote:
Hmmm. Maybe the rest of that list could stand a little review and verification, too.
The list was compiled by a few of us tinkering with cheap tubes. I did not verify every number on the list, so yes check carefully before plugging in.

Quote:
More confusing is why are 9DC and 9AE the same pin out? Are there others like them where two designations are used for the same pin out?
There are a few but I don't remember them all. I'm guessing that different manufacturers registered their new tubes with RMA or RETMA (both now part of EIA) at the same time and the duplicity wasn't caught. There were no computers then.

Octal: 7AC = 7S 8EP = 8ET

9 pin: 9AJ = 9DE

7 pin: 7BK = 7CC


Quote:
Making spreadsheets is boring. Very, very boring.
Tell me about it. 38 years as an RF engineer, spreadsheets and Powerpoint slides have become a way of life in big corporation engineering. It's not about the circuit design...it's "He who has the best presentation wins." The tennis player selling Canon cameras said it best years ago "Image is everything."

Quote:
I'm working on a four-tube 3.5 watt design that goes from sweet and clean to full metal fuzz with a broader frequency response than this one, and includes bass, mid, treble, and spring reverb for the $99 target.
Unfortunately to hit the $99 target with a long list of features, you are going to need a spreadsheet to determine how best to utilize the budget

Quote:
But the secret hidden within this tube has begun to reveal itself to me. And that, my friends, is exciting.
Remember, the published data was drawn up with the tubes intended operation in mind. Just about every tube mentioned in this entire thread was not intended for use in a guitar amp. Most were not even intended for audio. There are lots of secrets yet to be discovered in the tube world even though tubes have been around for a long time. This becomes more true when you allow judicious use of silicon. Screen driven audio power amps come to mind.
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Old 7th September 2011, 02:13 PM   #1030
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So has anyone else figured out for a reverb you can use the speaker frame as the sender?
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