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  Not So Subtle Sag
Posted by: Strelok - 18 minutes ago - Forum: Preamp Mods & Design - No Replies

Hi all you FireBottle lovers!



FireBottle... who came up with that name?



A long time ago I built a Sustainor Preamp.
Like I said so many times: this preamp rocks!


I tried new tubes in it, and they were doing a "new tube" thing.

They gave a sag that was *not* subtle!
The harder I hit the strings, the slower the sound came up.

It was fantastic!
After a while the effect was gone though.

As far as I have seen, the SUS kit works time based, there are a few resistors that set the time.
Can it do this kind of sag?


I have an EHX "Attack Decay", that one works by peaks.
When it detects a peak the preset attack and decay times are applied, so that is only based on preset times.

Fun Fact:
This thing can do something I have not seen anywhere else.
If you apply "poly mode" each note that you play gets its own attack and decay, even if you play multiple notes and let them ring!
I have no idea how they did this.
You would have to sample each note seperately as they are played and then play back a sample with the correct envelope.

But how can you extract the different notes?

Nice riddle to think about, but no solution available!



Strelok

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  Using chassis-mounted sockets with the kits
Posted by: K O'Connor - 04-12-2021, 04:25 PM - Forum: London Power Kits & Mods - No Replies

Hi Guys

Hobbyists often ask if they can use a chassis-mounted tube socket with the kits, to which the answer is 'yes', but with caveats.

The PCB layout incorporates the tube sockets and this controls the physical form of the connections to the sockets. All the parasitic capacitances and inductances are then controlled and stability is assured for the assembly. There is a further benefit that unit-to-unit consistency is assured even though most hobbyists will only build one of a thing.

If you really must use chassis-mounted sockets but want to use  London Power PCB project as the basis, then the grid-stop resistors should be mounted right at the socket pins and a wire link installed in those positions on the PCB. The wiring to each triode or pentode should just be #22 stranded wire, properly twisted. For example, each triode in a dual-triode needs three wires. You can solder the wires to the PCB end, say, then measure out more wire than the distance to the socket side to be wired; then cut the wires; then twist them starting at the anchored end and allow ALL 3 free ends to rotate as you twist; only then do you begin terminating at the socket. Of course, you can reverse this order and begin at the socket remembering to install the grid-stop between the grid wire and the socket pin. Each triode then has its twisted-triple.

Heater wires should be twisted unto themselves. London Power PCBs that carry dual-triodes accommodate both 6V and 12V wiring. 12V wiring is preferred for 12V-capable tubes, as TUT4 explains, and in that case you do not have to bring out the pin-9 wire. The PCB keeps the heater wiring away from the triodes but now you are changing the effective layout and need to do so with care.

DO NOT use multi-conductor shielded cable to the tube socket. The cable capacitance will kill the frequency response and you'll be replacing it with twisted hook-up wire, so save a step Smile

The same guidance applies to octal tubes, pentodes and tetrodes. With the latter, especially with transformer connections, the transformer connections can still go to the PCB unless it is neater to have them go directly to the tube socket. Remember that the screen-stop should be tied to the screen-pin at the socket. The PCB achieves this, but now you have to place the resistor on the socket in the traditional manner. Where 300V wire is okay for everything else, the plate and possibly the screen wires for a power pentode - tetrode should be rated higher, at least 1kV.

Have fun

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  Which cable?
Posted by: Strelok - 04-12-2021, 02:13 PM - Forum: Preamp Mods & Design - Replies (4)

Hello Tube Doctors!


I'm in the market for buying soms shielded cable.
I used Doug Hoffmans cable, but now I wnat to order at Mouser with the rest of the parts.

I can't find good cable there, what do you folks use?


Warm regards,


Strelok

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  S-PRE-2
Posted by: John Bourke - 04-08-2021, 10:49 AM - Forum: London Power Kits & Mods - Replies (1)

A few questions about the S-PRE-2 kit.  Hopefully Kevin can help here.

I'm stuffing the board, and I have ended up with two capacitors that I'm not 100% on.
   

Markings are (as far as I can tell) 471J on the blue green one, and 0.47 J100 on the red one.  The board has spots for a 470p (C7) and a 470n (C9).  My assumption is that the 0.47 on the red one is 0.47 microfarads, which means 470Nanofarads, and it is C9, which leaves the blue green one for C7.

Also - I assume there's nothing keeping me from doing the tube sockets off board?  Is 20AWG stranded good enough for that?

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  Stereo Reverb as in TUT2
Posted by: Strelok - 03-28-2021, 10:32 AM - Forum: Preamp Mods & Design - Replies (5)

Hi all!


I'd like to build the Stereo Reverb as in TUT2.
Has anyone done that?

Which Reverb Block would be best, the one in the LP Standard or the Standalone Reverb Kit?


Greetings,

Strelok

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  Spectrum Analyzers
Posted by: NCtubes - 03-09-2021, 12:34 AM - Forum: Test & Measurement - Replies (1)

Can anyone recommend a reasonably priced audio frequency spectrum analyzer which accepts electrical line level inputs?
Thanks,
Steve

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  EL34 glowing internally with signal...
Posted by: liquidair - 03-03-2021, 07:58 PM - Forum: Preamp Mods & Design - Replies (5)

Hi all, I have a project where I'm using EL34s (new Mullards) and I noticed that as I played I could see an orange glow through the hole in the plates that would pulse with the music. Is that normal? This amp has a b+ around 400-410 at idle and I have 1k 10W resistors on the screens (drawing ~5mA at idle), and I'm biased rather cool at 32mA. I don't really think I'm pushing it, but the screen resistors are getting pretty darn hot. I had another EL34 design with a higher B+ and 1k 7W screen resistors that I remember being able to touch after an hour of playing with the EL34's at max. Is there something I should check or am I just being a worry wart? Thank you all!!

(Sorry if this is in the wrong place, I didn't see a "Power Amp" section of the forum!)

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  Pricing help needed (please)
Posted by: NCtubes - 03-01-2021, 05:12 PM - Forum: Personal Projects - Replies (4)

Hey all,
I could use some input from you guys. I have been asked to build a few amp conversions in tolex covered head cabinets.  I need some opinions from other players about how much these would be worth to players to decide if it's worth doing. How much should I charge for these amps?
Thanks Guys for any input you can share.

Info on the amps is:

[font=Tahoma, Verdana, Arial, sans-serif]
https://youtu.be/4vVNFjWatKU

This amp was designed and constructed using the basic foundation of a 1960s (Akai M8) Roberts 770X tube reel to reel tape recorder. The amplifier circuitry has been optimized to specifically serve as a guitar amp rather than as hi-fi equipment. Where practical the original vintage components, including the tubes, have been kept.

There are 2 instruments inputs which share the common volume and tone controls. The 2 inputs however employ separate, and different, input stage tubes and therefore sound very different. The first input uses an EF86 (6267) tube. These tubes were used in 1960s vintage VOX amps, and are still used in some Dr. Z, Matchless, and other boutique amplifiers. The 2nd input uses a 12AX7 (12AD7) tube. 12AX7s are the most common preamp tubes used in guitar amplifiers such as Fender, Mesa Boogie, and Marshall. All of the tubes are the original vintage 1960s tubes. This amp is very quiet (background noise and hum) and breaks up nicely at reasonable volume levels.

The tone circuit uses a modified passive Baxandall/James circuit (Bass and Treble controls) similar to the type of tone stacks used in the original Ampeg, Orange,  and some Dr. Z amps. Additionally, a boost switch increases the gain and frequency response of the amp providing additional tonal flexibility.

The output stage is a single-ended class A power amp. This amp uses an EL84 (6BQ5). Single-ended class A amps were used in many lower power 1950s-60s Fender Tweed and Blackface amps and in Vox's AC-4, which also used the EL84 tube. The amp uses a 6X4 tube rectifier. This amp works great for rehearsal, small venue use, and especially studio recording.
[/font]


[font=Tahoma, Verdana, Arial, sans-serif]They look like this in the cabinet:[/font]
[font=Tahoma, Verdana, Arial, sans-serif]https://www.dropbox.com/s/5mveip4iprwp7ey/PXL_20201201_192712695.jpg?dl=0[/font]

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  5 Watt Tube Guitar Amp Conversion Project
Posted by: NCtubes - 02-18-2021, 03:41 PM - Forum: Personal Projects - Replies (10)

Here's a little 5 Watt tube rehearsal/ studio guitar amp that I converted from a 1960s tape deck for a few friends. It's been evolving over the past year based on their feedback.

https://youtu.be/Ya2bgr9mEtM

This amp was designed and constructed using the basic foundation of a 1960s (Akai M8) Roberts 770X tube reel to reel tape recorder. The amplifier circuitry has been optimized to specifically serve as a guitar amp rather than as hi-fi equipment. Where practical the original vintage components, including the tubes, have been kept.

There are 2 instruments inputs which share the common volume and tone controls. The 2 inputs however employ separate, and different, input stage tubes and therefore sound very different. The first input uses an EF86 (6267) tube. These tubes were used in 1960s vintage VOX amps, and are still used in some Dr. Z, Matchless, and other boutique amplifiers. The 2nd input uses a 12AX7 (12AD7) tube. 12AX7s are the most common preamp tubes used in guitar amplifiers such as Fender, Mesa Boogie, and Marshall. All of the tubes are the original vintage 1960s tubes. This amp is very quiet (background noise and hum) and breaks up nicely at reasonable volume levels.

The tone circuit uses a modified passive Baxandall/James circuit (Bass and Treble controls) similar to the type of tone stacks used in the original Ampeg, Orange,  and some Dr. Z amps. Additionally, a boost switch increases the gain and frequency response of the amp providing additional tonal flexibility.

The output stage is a single-ended class A power amp. This amp uses an EL84 (6BQ5). Single-ended class A amps were used in many lower power 1950s-60s Fender Tweed and Blackface amps and in Vox's AC-4, which also used the EL84 tube. The amp uses a 6X4 tube rectifier. This amp works great for rehearsal, small venue use, and especially studio recording.

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  Source/Part Number for Rack Mounting Brackets for Hammond Chassis?
Posted by: makinrose - 01-20-2021, 01:12 PM - Forum: Personal Projects - Replies (4)

Does anyone have source and/or part number for rack mount brackets like those illustrated in the 800 chapter in TUT3?  I'm thinking about making an amp into a 17"X10"X3" Hammond Chassis and rackmount it. Thanks!

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Come in where it's warm!
A warm welcome to tube amp modding fans and those interested in hi-fi audio! Readers of Kevin O'Connor's The Ultimate Tone (TUT) book series form a part of our population. Kevin O'Connor is the creator of the popular Power Scaling methodology for amplifiers.
Please remember these three principles: respect, sharing, community.
Not familiar with The Ultimate Tone book series? See discussion topics, or click here to visit London Power/Power Press Publishing.

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