London Power ad

Search the Forum

(Advanced Search)

  Question about filament transformer for bias supply in a Power Scaled Amp
Posted by: makinrose - 02-06-2020, 02:05 PM - Forum: Power Scaling - Replies (2)

This might be dumb question....I'm typically using a DC elevated heaters like what is shown in TUT 3 and TUT5. If I need to run a filament transformer for the bias supply off of the heater supply do need to remove the DC elevation or use caps to block the DC?  Huh

Print this item

  YBA-1 bridged T circuit
Posted by: jmcd - 01-05-2020, 04:58 PM - Forum: Preamp Mods & Design - Replies (9)

I picked up a lovely Traynor YBA 1 that has a bridged T circuit between the second and third gain stages along with a plate-driven tone stack. I've read through the TUT3 chapter on the Bass Master, but I'd like to know more about the bridged T circuit (what it does, how it does it, and what sorts of component value changes are possible).

[Image: OjXgYt6l.jpg]

Print this item

  Tube Microphone Pre-amp Inputs
Posted by: makinrose - 12-25-2019, 01:32 PM - Forum: TUT Q&A - Replies (3)

I've been thinking about building some microphone pre-amps for recording purposes. Since the microphones I'm using are Lo-Z I was looking at matching transformers and at the cathode input circuit from TUT-2.  I've built pre-amps with matching transformers but have not had any experience with a cathode input circuit on a mic pre-amp before.  Are there advantages or disadvantages to that circuit versus a transformer?  Do they sound different?  Thanks guys!

Print this item

  50 watt amp project
Posted by: TiCatFan - 12-06-2019, 08:43 PM - Forum: Personal Projects - Replies (10)

Hey all;

looking for some help, i have put together the power supply kit PSU TPA and the power amp PA66, 50 watt version. i had the power supply working in a very prototype way, transformer and power supply board laying on my bench , but working. decided to add a power switch, it works, output transformer, power amp and front end. Hooked up an output jack and impedance selector, kept the options to a minimum at this point, master volume and presence control ( the ones available on the PA66 board ). Stuffed it in a hammond chassis, plugged it into the power limiting safety socket and turned it on, no tubes.

But, it doesn't work. I am trying to trace through the circuit to find the problem but thought I would ask on the forum if someone might know of likely suspects I should look at.

What I do know is, when I turn the amp on the light bulbs on the safety socket come on and stay on, fairly bright. The fuses do not blow, these are the fuses supplied with the kit and I am not sure offhand the wattage or blowage?? of the fuses. The panel LED does not turn on, nor does the 12v fan. Kind of afraid to leave it on long enough to check for voltages anywhere, I have left it on for a 10 count a couple of times, nothing hums or smokes or anything.

Is it possibly a messed up MOSFET?, any ideas on what to look at and how would be greatly appreciated. I have been trying to follow the AC supply but I also wonder if a short to ground would take out the fuses. What might draw power but not blow up the amp???

Greatly appreciate any help I can get...


Print this item

  Hello from England
Posted by: The_only_Tinners - 11-29-2019, 02:38 PM - Forum: New Member Introductions - Replies (2)

Hello from across the pond. I've been fixing up old amps, and building the occasional one myself and trying to take it a little more seriously. The next build is more ambitious, great to have the wealth of knowledge available here Smile

Print this item

  Hammond chassis mounting question
Posted by: FormyxAmps - 11-27-2019, 05:57 PM - Forum: Wiring - Replies (4)

Hi all,

For mounting a usual Hammond chassis in a wooden enclosure MArshall-style, I use angled brackets mounted on the chassis using blind rivets where the whole construction is then fastened using bolts and screws, but I've always wanted to have a system that uses cage nuts instead...

How would you mount it? What hardware would you use?

P.S. Couldn't find a more relevant subdir, hope its is ok to post here. Wink

Print this item

  PSU testing
Posted by: SGillespie - 11-19-2019, 05:19 AM - Forum: Power Supplies - Replies (6)

Hey folks,

So I've built my first London Power standalone preamp kit and unsurprisingly it doesn't work. This is my first amp project; I'm used to building pedals. But I have to start somewhere. It's the M-Pre (hot rodded 800 version) with the Pre-PSU for two tubes.

So what I did was build it like I build a pedal. Basically followed the instructions, put it together and turned it on. Of course in hindsight I should hve been constantly testing as I went, but as i said, it's my first one.

So the tubes didn't come on and of course there's no sound. So what should I do first? Check the psu, I guess. So what would be the best way to go about that. I have some basic electrical knowledge (mostly safety stuff) and of course a dmm. Any advice would be greatly appreciated.



Print this item

  New kid
Posted by: SGillespie - 10-28-2019, 08:30 AM - Forum: New Member Introductions - Replies (4)

Hey All,

I'm really looking forward to getting into building my own amps. I've been a guitarist (sometimes bassist) for 30+ years, played in numerous bands (none famous) on both sides of the Atlantic; first in Canada (home country) and now in Belgium (long story Big Grin )

Don't be surprised if I end up asking some real noob questions  Blush


Print this item

  Questions about Super Scaler Project in TUT5
Posted by: makinrose - 10-20-2019, 01:15 AM - Forum: TUT Q&A - Replies (2)

I've been fascinated with the Super Scaling project in TUT 5 but have few questions:

A.  As the chapter on Super Scaling indicates would I get about a 6 fold increase in power? So andamp that was 10W would be 60W through it, right?  

B. Power possible would be limited by the output power of the Super Scaler's OT?  So how much power is possible? 

C. Does the power tube type color the sound a lot? 


Print this item

Posted by: NGW - 09-11-2019, 12:45 AM - Forum: Preamp Mods & Design - Replies (10)

Hi Ultimate Tonesters,

I have had to shelve amp work for most of this year, due to other pressing issues, but I am now getting back into it.
The TUT Forum is looking a bit quiet; where are you all?

I have a query regarding bypassing a Gain Stage, which is a bit foreign to how I would arrange a Drive stage, so this is not something I have tried before.

The attached circuit shows a 4 stage preamp that uses 3 for Clean and adds the 2nd stage (V2B) for Drive.
The cct. is shown in Drive mode and when switched to Clean, Relay 1B enables a full bypass of the 2nd stage. 

In Clean mode; would you advise grounding the output from V2B, as shown with Relay 2, to remove any possible signal or noise from V2B entering the grid of V1B; or will the Clean Bypass be sufficient to ensure uncorrupted Clean sound?
Modifying the PCB traces and installing wiring to enable Relay 2 to ground V2B output is not a fun job but, if it is advisable, I will do it rather than have the clean sound compromised.
The owner loves the Clean sound and doesn't want to lose it.

Thanks for any advice,


Print this item

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.

Tube Amp Forum Hosted by London Power
London Power logo