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21

Tube Amp Building - Tweaks - Repairs / Re: Deluxe 5E3 tone stack

« Last post by kagliostro on September 05, 2025, 03:58:17 pm »

A triode has a relatively low internal resistance (ri) (on the order of tens of kΩ).
This makes it suitable for driving resistive/capacitive loads such as a tone stack, which is typically a passive attenuator with resistors in the 100 kΩ range and capacitors of various values.

A pentode, on the other hand, has a very high internal resistance (hundreds of kΩ up to several MΩ).

In practice, it behaves almost like an ideal current source, with very little ability to supply current to a “heavy” load.

A classic passive tone control (like            Fender/Marshall/Vox) has:

A typical working impedance around 30–50 kΩ at mid settings.
A signal loss of about 10–20 dB, even without extreme adjustments.
A strong dependence on the source impedance: if the driving stage has high output impedance, the tone stack becomes ineffective or alters the frequency response unpredictably

If you put it after a pentode, which has extremely high output impedance, what happens is:

The pentode cannot provide enough current to properly drive the potentiometers and capacitors in the network.
The tone stack heavily loads the anode signal gain collapses and the frequency response becomes unstable.
The result is a choked, unmanageable sound.

Franco

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Tube Amp Building - Tweaks - Repairs / Re: Oahu Tonemaster-Hum and 21khz distortion

« Last post by wsscott on September 05, 2025, 02:58:10 pm »

Found the fix for the hum.  In doing the poke test I found that the .05uf cap connecting the Tone Pot to Ground had a bad lead.  I replaced the cap, and the hum is gone!!

Thanks for your help.

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Other Topics / Re: Anybody watching Gold?

« Last post by shooter on September 05, 2025, 01:55:51 pm »

this is a drone stock, but the premise works across the board, metals, money, stocks
this gap was 6 weeks ago, it's positioned to start a long slow run up, just like metals will.

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Other Topics / Re: Anybody watching Gold?

« Last post by EL34 on September 05, 2025, 12:55:34 pm »

The red lines are where Silver and Gold will retrace to fill the gaps

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Tube Amp Building - Tweaks - Repairs / Re: Deluxe 5E3 tone stack

« Last post by kagliostro on September 05, 2025, 12:13:52 pm »

Ciao Lectroid

When I've seen your first schematic with the pentode and the Tone Control I was in doubt if you  were using it only to show the kind of Tone Control you were interested to put on your 5E3 (with triode as V1) or to really build it that way with the V1 pentode

So I posted about the loss of signal if a pentode Is followed by a Tone Control

That happens because of the impedance of the pentode that Is loaded in an havvy way

Now accept it as is, don't remember at the moment the exact tenichal explanation, I learned this thing  years ago, because I noticed that only very, very few amps that has a pentode adopt a Tone Stack after a pentode and investigated

I'll go to reftesh my memory and say more later

If you are interested to see one of the few schematics with a V1 pentode followed by a Tone Control give a look to the Dr Z Route 66 schematic I attach here

---

The schematic I posted is a mix of mod we found on the web and mix together, years has past since there and don't remember the source of the double Tone Control arrangement, we were plagiarizers not engeeners

Franco

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Tube Amp Building - Tweaks - Repairs / Re: Deluxe 5E3 tone stack

« Last post by Lectroid on September 05, 2025, 10:38:47 am »

If anyone's interested, below is the full schematic of my amp as built 

Leo ... was trying to get them to sound cleaner ... If you make it three preamp triodes before the cathodyne, you will get even more distortion - which may well be your goal YMMV. (If you put a pentode in there - like you have in your schematic - even more distortion)

I do like this amp because it slips so smoothly into distortion as I turn up the Volume past 4-5.  If that's due to the pentode topology, more power to it.    The design is 95% stock Bell&Howell projector amp.  I changed the originsal Tone circuit, to be frank, just because I couldn't understand it at the time.  Not sure I do do now, beyond it being a series of RC high-pass and low-pass filters to, I suspect, deal with a rather harsh operating environment inside the projector.  I know some guitarists revere the tone of the unmolested B&H and I sort of regret my noobish butchery.  But I'm happy with the result.

With the original arrangement you get treble cut and boost (if the vol pot is not at maximum). But with your arrangement you only get treble cut, and also volume loss, so it's a less versatile configuration.

So--turning up the volume sends less and less signal through the tone pot, and send more signal to the grid of V2a.  I'd guess this also sends less signal through the Tone pot for filtering. So, in the standard 5E3 Deluxe, higher volume also comes with a lowered ability to control tone. 

Only one consideration
A pentode has more gain than a triode but the signal loss Is higher if a pentode Is followed by a Tone Control than what happen to a triode
Franco

Why is that?  I think others here alluded to that also.

I like your schematic, with that interesting volume/tone arrangement.  Are the extra caps on the volume and tone pots put there to provide a "bright" option, like Fender did?  Only not on a switch, but controlled by a pot?


Everyone, thanks for all the discussion.  I've learned a few things.



 

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Tube Amp Building - Tweaks - Repairs / Re: Deluxe 5E3 tone stack

« Last post by Platefire on September 05, 2025, 10:24:31 am »

OK, I found it! sluckeys explanation on how the bright channel effects the normal channel as follows:

Assume no signal on the bright channel. The 'blue' indicates the normal signal path and the 'gold' indicates tone filters.

Look at Figure 1. The tone pot and .005µF cap form a variable series shunt filter connected directly between the normal signal path and ground.

Look at Figure 2. The bright channel volume pot and the 500pF cap interact somewhat with the normal signal also. Imagine the tone pot wiper at the top end of the pot and the bright volume pot at it's bottom end. The 500pF cap is shorted out in this case and it's effect on tone is minimal. Now crank the bright volume pot to the top and you will see that the 500pF is now connected directly between the normal signal path and ground, shunting some high frequency signals to ground. Moving the bright volume pot between extremes varies the amount of attenuation to the high frequencies, acting like a tone control for the normal channel. The effect is not nearly as noticeable as the real tone pot, but you can hear the effect.

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Tube Amp Building - Tweaks - Repairs / Re: Questions about Rehabilitating a 65 Super Reverb

« Last post by stratomaster on September 05, 2025, 09:17:00 am »

wouldn't it be easier with an oscilloscope?

Not easier, but definitely more thorough and better for your skillset long term. I recommended the multimeter because the mechanics of taking AC voltage measurements are identical to the DC ones you're already taking.

how hard is it to do basic signal tracing with an oscilliscope (ie, for a newbie)?

getting familiar with the scope would be the challenge. It's worth the effort in my opinion, but as a beginner who might not take it much further that fixing an amp or two or a kit build, it may not be worth it. There are concepts like triggering, DC vs AC coupling, peak to peak vs RMS, having to keep track of probe multipliers, etc that can trip people up until they get used to them.  If you're wanting to learn, then there were several good instructionals and explainers on YouTube.  And with the flood of inexpensive and feature rich scopes on the market the barrier to entry has never been lower.

what affordable oscilloscope would anyone recommend for a complete beginner?

Any scope you can afford will be able to do amp work. Our frequencies are so low that any single channel scope with a 10x probe will to most anything you would need. It's nice to have a second channel, and newer digital scopes have the ability to do much of the math for you on the waveforms, so if you're not used to working with a calculator by your side, that's a plus.  I recently bought a $35 FNISRI (or something like that) scope on Amazon just out of curiosity.  It would easily do the signal tracing we're discussing, but the UI is a but clumsy for someone like me used to knobs and switches.

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Tube Amp Building - Tweaks - Repairs / Re: Deluxe 5E3 tone stack

« Last post by kagliostro on September 05, 2025, 07:29:36 am »

Don't know if this can be of your interest


This is a 5e3 build from scratch that we planned few years ago at DIYItalia and was build by a friend with success

Note that each channel has its own Tone Control with different arrangement and values, channels can be joined at the input

Franco

p.s.: FXLoop was borrowed from one of the Mr Merlin's books

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Other Topics / Re: Meme of the day

« Last post by shooter on September 05, 2025, 07:27:34 am »

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