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Old 3rd September 2011, 05:48 AM   #1011
tubekit is offline tubekit  United States
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The 6EB8 does have quite enough gain to produce useful bluesy overdrive distortion.

The triode has an AF of 100. The pentode has a mu of 12,000.

If you're going to use a cheap output transformer, you need to use the right cheap output transformer.

First stage operating point, interstage loading, screen voltage and bypass, pentode bias voltage, all of these are critical to getting the desired result.

It has been done.

There are many people who know that the gain of a 6EB8 produces quite useful and satisfying distortion. It isn't a stand-alone Fuzz Face, it isn't a Big Muff Pi, it isn't a Rat. It won't get you into heavy metal all by itself.

But it is a stand-alone practice amp with the "right" amount of volume and distortion.

It will get you into some pretty heavy Blues with a standard single coil pickup.
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Old 3rd September 2011, 01:44 PM   #1012
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Quote:
Originally Posted by tubekit View Post
The 6EB8 does have quite enough gain to produce useful bluesy overdrive distortion.

The triode has an AF of 100. The pentode has a mu of 12,000.

If you're going to use a cheap output transformer, you need to use the right cheap output transformer.

First stage operating point, interstage loading, screen voltage and bypass, pentode bias voltage, all of these are critical to getting the desired result.

It has been done.

There are many people who know that the gain of a 6EB8 produces quite useful and satisfying distortion. It isn't a stand-alone Fuzz Face, it isn't a Big Muff Pi, it isn't a Rat. It won't get you into heavy metal all by itself.

But it is a stand-alone practice amp with the "right" amount of volume and distortion.

It will get you into some pretty heavy Blues with a standard single coil pickup.
Not much into heavy distortion, more inclined to the edge of breakup or rock tones. Mind you ACDC and the Ramones can be a lot of fun, a pedal with boost might be in order. Not being familiar with the tube I would be interested hearing some clips of it.
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Old 4th September 2011, 02:34 AM   #1013
tubekit is offline tubekit  United States
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Hi Printer,

This was not a reply to your post, but to others.

And forgive me, but I meant to say ". . . has a gm of 12,000 . . ."

I do understand the difference between transconductance (gm) and amplification factor (mu).

Although it is classified as a sharp cutoff pentode, an examination of its graph of grid voltage vs. transconductance and plate current will show significant differences between the amount of gain obtainable at various operating points.

In fact, the maximum gm of this pentode goes all the way up past 16,000 before reaching saturation.

An audio clip is on the to-do list, but not available yet. I need to rehearse some rust out of my fingers first.

I could just bang on the strings to prove my point, but it wouldn't be very elegant.
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Old 5th September 2011, 04:06 AM   #1014
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I am at work from 8 AM to about 7 PM every week day. Computer use is monitored and forum posting is frowned upon. In my last post I attempted to correct some incorrect statements another poster made about something I said, and provide some information about the 4 tube version of AMP1.0 now called AMP1.2. It took me about 20 minutes to compose and type my post into a cell phone and the moderator about 20 seconds to delete it. I do not have 20 minutes to waste during my work day, so I will refrain from posting until I have something important to contribute and a real unmonitored computer to do it from. This will be rather infrequent for the next 3 or 4 weeks.

AMP 1.2 is alive and working. Power output is 2 watts when the controls are set for a clean undistorted output. Power output is just over 3 watts at full crank. There are two controls volume, and tone / distortion. The tone / distortion control can provide a wide wange of sounds from clean to cranked. No you aren't going to get a full metal racket from a 2 watt amp, but I did manage to get some acoustic feedback with the guitar about 6 inches in front of the speaker. Total parts cost is less than $50.
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Old 5th September 2011, 04:58 AM   #1015
ChrisA is offline ChrisA  United States
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Quote:
Originally Posted by TheGimp View Post
That is an interesting idea ChrisA. Unfortunately with the controls up it would require the channel to be vertical. Sliding the chassis down would impinge upon the speaker frame, so the speaker would need to be removed before removing the chassis.
I've used this method on "controls up" amps too. Look at the Fender Baseman, Champ of any of the tweed era amps. They use a cut out on the top panel. I do it just like Fender did except I place a pair of small wood blocks under the chassis.

You can see in this photo (50's vintage 5F1) that Fender used two machine screws from the top. But I like to add a pair of wood blocks under the chassis and glued to the cabinet sides. Heuse wood for the top plate that was thick enough that one could set the amp upside down on the floor and not damage the controls
http://myfenderchamp.com/wp-content/...7/IMG_9300.jpg
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Old 5th September 2011, 03:48 PM   #1016
Cassiel is offline Cassiel  Libya
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Quote:
Originally Posted by tubelab.com View Post
I am at work from 8 AM to about 7 PM every week day.
Man, that's a lot.

Quote:
Originally Posted by tubelab.com View Post
It took me about 20 minutes to compose and type my post into a cell phone and the moderator about 20 seconds to delete it. I do not have 20 minutes to waste during my work day,
Now you're talking. Moderators panic easily, not a funny job to be a chaperone. It's just an observation - I'm not annoyed at them.

Well, last Friday I did try out some cheap speakers ( a Celestion, a Beyma and some vintage ones with alnico magnets) and I also did some recordings. Pretty disappointed with the final results. Clips need editing, it just doesn't sound right. I was pretty happy with the live sound though and I've found out that the secret lies in the OPT and speaker combo. Different amp designs don't make that much of a difference. I'm busy with others things so I won't be contributing here much either. I'm curious about the one tube amp (tubekit) and maybe I will buy that tube to check it out.
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Old 5th September 2011, 05:44 PM   #1017
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I could see why they did some editing. Already it is a hundred page thread (does that mean the value is increasing, less than a buck a page) more or less on topic. Doubt things could disintegrate to the point of some of the topics I oversaw on another site (trying to back out of my obligations there so I can play more with this guitar thing).

Now rather than empty content in this post, thought I would share a simple Champ type circuit I want to build. The output tube/transformer could be whatever turns your crank, the interesting little bit is the tone control. A DPDT switch can give you the option of having the tone control between the first and second stage or between the second and the output tube. I did the Master volume like a Fender 5E3, rather than as a voltage divider to decrease the signal to the power tube it loads down the second stage and most likely screws around with the frequency response. To give it some more complexity it is inside the feedback loop more than likely messing things up some more. The transition where the feedback runs out of gain might make for some interesting sounds.

The part values are a starting point for now, maybe get to assembling it tonight. Looks like the kitchen is going to be a bigger job than I expected (mind you that is probably why I have not tackled it before now), it is getting in the way of me playing.


Click the image to open in full size.
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Old 5th September 2011, 10:16 PM   #1018
tubekit is offline tubekit  United States
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Default Deja Vu all over again

Quote:
Originally Posted by Printer2 View Post
going to be a bigger job than I expected
Don't know anything about your kitchen project, but those words have a familiar ring for some reason.

I seem to remember someone having said (or having tried to suggest) something like that about Topic 1 way back at the source of this 100+ page thread.

The pronoun was different, though.
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Old 5th September 2011, 10:38 PM   #1019
tubekit is offline tubekit  United States
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Default Tubekit's Amp Schematics

Don't know what happens to business after giving this away, since I don't make circuit boards, just create a margin by buying wholesale, but I once said I would submit this, and I keep my word.

This is the revised amp, for international use. It's "beefier" than the original because of higher plate voltages.

It works as claimed--here and elsewhere.
Circuit1.jpg

Circuit2.jpg

Circuit3.jpg
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Old 5th September 2011, 11:40 PM   #1020
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Don't know anything about your kitchen project, but those words have a familiar ring for some reason.
Oh you have asbestos also?
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