Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Boyuu EL34 A9 Tube Amp
Boyuu EL34 A9 Tube Amp
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 17th June 2018, 06:53 PM   #391
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Boyuu EL34 A9 Tube Amp
Hi Alllensoncanon,
Using a resistor in the line is a time honoured way to arrest surge currents and is quite safe to do. You just build the circuit on a PCB or tag strips just like they have done for nearly a century. Done properly it is no more dangerous than a bucking transformer.

-Chris
__________________
"Just because you can, doesn't mean you should" my Wife
  Reply With Quote
Old 17th June 2018, 09:43 PM   #392
6A3sUMMER is offline 6A3sUMMER  United States
diyAudio Member
 
Join Date: Jun 2016
A line voltage dropping resistor should rated to be able to handle at least 3 times the power ((I)squared x R) caused by the amplifier current draw.
The resistor should be in a metal enclosure (the amp or an auxiliary metal box).
There must be room for the resistor to give off its heat.
All construction should be according to electrical safety rules and regulations.

A dropping resistor example:
240V line - 220V amplifier = 20V drop required in the resistor.
Suppose the amplifier draws 0.8 Amp current.
20V/0.8 Amp = 25 Ohm dropping resistor.
(0.8 Amp) Squared x 25 Ohms = 16 Watts, use a 25 Ohm 50 Watt resistor.
This resistor either needs to be in the amplifier metal case, or a separate metal box.
In either case, the resistor should be connected After the fuse(s).

I suggest that you use 2 fuses in series:
A fast blow that is just large enough so it does not blow during the amplifier inrush current at turn-on.
A slow blow that is just large enough so that it does not blow from the current draw of the warmed up amplifier.
Safety first.

By the way, a line bucking transformer is a good idea too. It is more efficient, generates less heat than using a line dropping resistor. But it also should either be contained in the amplifier, or in a metal box.
And it must be connected After the fuse(s).
A240V to 20V transformer would work to buck 240V down to 220V (but only if connected in Buck phase, otherwise you get Boost phase and 260V!).

Last edited by 6A3sUMMER; 17th June 2018 at 09:48 PM.
  Reply With Quote
Old 17th June 2018, 10:03 PM   #393
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Boyuu EL34 A9 Tube Amp
Hi 6A3sUMMER,
Power is just I*V. At any rate, your post is good and I agree with what you are saying. Some resistors will mount to the metal case and use that as a heat sink. They are rated for that differential and of course the case would be grounded just in case the insulation fails.

The resistor is small and doesn't radiate 60 Hz hum, that's why they are so popular. A bucking transformer would need to be mounted in an external box for audio equipment.

-Chris
__________________
"Just because you can, doesn't mean you should" my Wife
  Reply With Quote
Old 17th June 2018, 10:44 PM   #394
Alllensoncanon is offline Alllensoncanon  United States
diyAudio Member
 
Join Date: Mar 2017
Location: NorCal, East Bay
Boyuu EL34 A9 Tube Amp
I see a resistor that drop 10% of the voltage will also generate 10% of the heat. 10% of 100W is not a small number to deal with. In a mishap (ie. Someone working on a power line outside), that number will only go higher. It can also be a thermal run away trap if that resistant go up with age and heat. Yes I agree, if that resistor is managed properly it can be safe. Properly not a good idea on an entry level Boyuu EL34 amp.
  Reply With Quote
Old 18th June 2018, 01:41 AM   #395
6A3sUMMER is offline 6A3sUMMER  United States
diyAudio Member
 
Join Date: Jun 2016
1. anatech,
and
2. Alllensoncanon,

1. Agreed, power = I x V.
But power also = (I)squared x R

And, we want to drop 20V with a resistor that has 0.8A through it.
R = V/I
R = 20V/0.8A = 25 Ohms

And, 20V x 0.8A = 16 Watts
And, (0.8A x 0.8A) x 25 Ohms = 16 Watts, just another way of saying the same thing (same circuit).

If you want the resistor to not smoke or at least discolor, use a wattage rating of at least 3x the power it will dissipate (I usually use 5x just to make resistors run cooler; more mass and more surface area).

2. Someone whose only experience is wiring a Boyuu amp, may not be up to safely building a metal box with 2 fuses, a Buck transformer, and power lead connections and wiring; or the same parts except a resistor instead of a Buck transformer.
I only mentioned resistors and Buck transformers for those who can safely do that sort of work.
But . . . that goes for all the threads on this web.
Safety first.

IMHO, using an amplifier transformer that is made for 220VAC and powering it with 240VAC is going to make it have 10% more power loss due to the core magnetization, and up to 21% more loss due to the Isquared x R loss of the DCRs of the primary and all the secondaries. That will make the amp power transformer run hotter.
How safe is that? Depends on how much margin was engineered in.

Last edited by 6A3sUMMER; 18th June 2018 at 01:47 AM.
  Reply With Quote
Old 18th June 2018, 02:33 AM   #396
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Boyuu EL34 A9 Tube Amp
Hi Alllensoncanon,
Quote:
In a mishap (ie. Someone working on a power line outside), that number will only go higher.
We can't design for every eventuality, nor can we condemn a hobbyist as incompetent either.
Quote:
It can also be a thermal runaway trap if that resistant go up with age and heat.
No, that doesn't happen with high power resistors. The increase is measured in ppm, so thermal runaway doesn't happen in any practical form.
Quote:
Properly not a good idea on an entry level Boyuu EL34 amp.
Considering the voltages that the circuits run at, I don't think the resistor is a major concern. There are so many ways a person can cause a fire or kill themselves working with anything that is AC powered that we can't single out a resistor as being a major risk. Each and every person who elects to work on things above a certain voltage level or power level is accepting a reasonable level of risk. We have clearly stated this in the notes we require members read for their own safety.

Dropping resistors on the AC line used to be quite common in industry. Pressure to make equipment efficient has curtailed that practice, same for buck transformers. Anyway. If you are going to argue safety, the bucking transformer is also out as being too dangerous for people to work with. Especially as a permanent solution. Therefore they should be forced to use a different transformer?

-Chris
__________________
"Just because you can, doesn't mean you should" my Wife
  Reply With Quote

Reply


Boyuu EL34 A9 Tube AmpHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Boyuu hifi Equis A10 EL34B+6N2 SE Tube Amplifier with 5Z4P rectifier: review and mod ygg-it Tubes / Valves 55 21st January 2018 03:21 AM
My new el34 + 12ax7 VCT amp. (Need Ideas For my first headphone vacuum tube amp Too~) briansune Tubes / Valves 10 12th July 2013 05:33 PM
FS: DIY EL34 / 6SN7 Tube Amp john65b Swap Meet 2 12th March 2012 02:02 AM
EL34 tube amp that needs work on el34ecc88 Tubes / Valves 0 17th December 2008 08:05 AM
EL34 vs. 6L6GC for 1ST DIY Tube Amp? pjkunz Tubes / Valves 4 17th December 2001 02:51 AM


New To Site? Need Help?

All times are GMT. The time now is 10:28 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki