DIY Audio Projects Forum
 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

DIY Audio Projects Forum

Welcome to the DIY Audio Projects Message Forum. Use these forums to discuss Hi-Fi audio and to share your DIY Audio Projects. Registration is free and required to post messages and view the file attachments. Registration will only take a minute and registered users do not see any advertisements. After you have completed the online registration process, check your email (including spam/junk folder) for the verification email to activate your account. New members are under moderation - so your posts will not be visible until approved by a moderator. See the Read Me 1st, Forum RULES and Forum FAQ to get started on the forum.

It is currently 21 Aug 2018, 07:04

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 11 posts ]  Go to page 1, 2  Next
Author Message
PostPosted: 08 May 2017, 18:28 
Offline

Joined: 29 Jun 2016, 15:59
Posts: 41
Hi all. Hope that you can clear this for me.

I am rather new to tube projects and most likely this is normal. I have read somewhere of startup voltage surge in the power supply. I use solid state diodes.
I built an integrated stereo amp and recently a phono preamp. Both using vacuum tubes of course. They work well.

However, recently I realized that when turning on the phono preamp the B+ voltage goes up to ~345 V and then slowly stabilizes at 270 V (no load), which is what I designed it for. I have not done the same measurement for the amp. But, noticed that the speaker drivers move significantly when I power-up the amp. I assume that this is due to the same startup surge action.
The caps and resistors have specs that go beyond the nominal voltages. Thus, I am not too concerned. Or should I? Is this something that should be corrected?

Any help is appreciated. Thanks,

Danny


Top
 Profile  
 
PostPosted: 08 May 2017, 21:09 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 3749
Location: Arizona, USA
Hi, An ever popping up question. The answers you get are mixed. In all my non-power amps and low power amps I do not control the initial over voltage. With the components I use they will handle the voltage easily. The actual circuitry is unharmed. For the large power amps I do make provision for the start up. Since all of them have solid state supplies that if not loaded would go well over 500 volts on start up and I prefer not to have to use the more expensive caps for over that limit I put in a delay. Typically about 75 seconds. A bit long perhaps but it insures the tubes are warmed up. This delay also tends to preclude start up thumps in the speakers. I interrupt the power before it gets to the filters. With the filter values chosen there is a finite ramp up time that is sufficient to sort of slow start the B+. Granted very short, but sufficient to prevent start up thumps in the output. A good thing when some of the amps can deliver a solid 40-45 watts rms. So my suggestion is to use delays when there is a reason to do so and not worry about it the rest of the time.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 09 May 2017, 01:20 
Offline
User avatar

Joined: 08 Aug 2009, 03:11
Posts: 2225
Location: Chilliwack, BC
There's inrush current limiters, but have to be chosen wisely as they all have voltage drop.

Then there's the old fashioned way of a power resistor that after 3-5 seconds is bypassed with a relay. I use that for when the running draw can tolerate zero voltage drop.

Cheers!

_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


Top
 Profile  
 
PostPosted: 09 May 2017, 09:03 
Offline
User avatar

Joined: 01 Jun 2013, 09:05
Posts: 655
Just my thoughts,

There are many variables in circuit design that may require anti surge one being direct coupling of tube circuits to prevent HT without heaters running and over voltage on Grid to cathodes.
However there is a school of thought that heater and HT on together controls over voltage on PSU caps.
The days of the valve TV<<a billion TV sets can't be wrong.

However, I use transient inrush suppression thermistors on the mains input to the power transformer.
This is really a must with toroid transformers particularly on high power or the mains switch will weld closed.
I use inrush suppressors on the negative rail of many circuits to protect the PSU caps.
With tube rectifiers this sounds like a none issue but I use them there as well... :D

So I guess the idea is does the circuit have any anomalies that need controlling.
The voltage is not so important as long as its not over voltage as the inrush surge, which is as bad as using a short to discharge a power cap and can do damage.

If your not sure fit inrush suppression on the primary of the mains Tx it won't do any harm and reduces magnetisation current.
You can often hear the surge on a power Tx you get a loud buzz or hum for about a second..then it goes quiet.
The problem with this is it can loosen the iron circuit over time and you get a mechanically noisy power Tx. Moot on toroid Tx's but they tend to weld the power switch.. :D
Something between 10-40 ohm inrush suppressor with correct current rating..you can series inrush suppressors to get a correct value.
You can calculate it or just try a 20 ohm. If its noisy perhaps CL60 etc(remember they get warm keep away from other components)
Link:
http://www.mouser.com/ds/2/168/920-325D-LR-245176.pdf

Regards
M. Gregg

_________________
What is the sound of one hand clapping?


Top
 Profile  
 
PostPosted: 10 May 2017, 12:02 
Offline

Joined: 29 Jun 2016, 15:59
Posts: 41
Guys,

Thanks for the replies. I would appreciate some more help.
Please, note that in my amp I use separate switches for the heater elements (which I turn-on first for ~30 secs) and B+ (which I turn-on afterward).

1) M. Gregg uses inrush suppression current limiters, which seem to be the easiest solution. Is this how I would wire it? See attachment. Sorry for the sloppy diagram. I am just trying to get my point across quickly.
2) Geek uses a power resistor that after 3-5 seconds is bypassed with a relay. Any examples/schematics?
3) Bruce uses delays. Again, Any examples/schematics?

Any help is greatly appreciated. Thanks,

Danny


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.



Top
 Profile  
 
PostPosted: 10 May 2017, 16:36 
Offline
User avatar

Joined: 01 Jun 2013, 09:05
Posts: 655
Yes,

The inrush suppressor goes in series with the primary of the power Tx as you show it.

I normally find 20 ohms does it but you could try CL60/CL70 or even CL80.
Remember they run warm and they are at Mains potential so must be mounted where the heat wont effect other components.
Depending on the electrical regs in your country you may need a two pole mains switch.
On a high power amp I used two CL60's in series.
Some people say that they want the lowest ohmic value under hot conditions, but this doesn't allow for hot restart surge.
ie the amp is powered down then immediately switched on with the suppressor still warm. (its bad practice but it happens).

You can also use MOV suppression on both the primary and secondary to remove back EMF turn off transients as well.
Another way is using tran-sorb diodes like Russ Andrews super clamp, There is always more..

_______________________________________________________
Using inrush suppression can also prevent having to use oversized fusing due to fuses blowing during power transformer magnetisation.
Basically the way they work is they have highest resistance when cold, then at power on they heat up due to voltage drop across the device which is highest at magnetisation. As they warm up the resistance drops and voltage drop reduces..you probably already know this.

Regards
M.Gregg

_________________
What is the sound of one hand clapping?


Top
 Profile  
 
PostPosted: 10 May 2017, 23:26 
Offline
User avatar

Joined: 08 Aug 2009, 03:11
Posts: 2225
Location: Chilliwack, BC
Danny wrote:
2) Geek uses a power resistor that after 3-5 seconds is bypassed with a relay. Any examples/schematics?


Here you go!

With power transformers over 500VA class, you want the resistor to have a high surge current capability (the white cement ones will fuse). A "Brown Devil" or the like.

Cheers!


This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.


_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


Top
 Profile  
 
PostPosted: 11 May 2017, 11:30 
Offline
User avatar

Joined: 01 Jun 2013, 09:05
Posts: 655
The good thing about the timed resistor surge protector, is that at each start you get a guaranteed resistance at every start.

I prefer inrush suppressors because its simple and you don't need a supply for a timing circuit.
However whatever floats your boat. Some people combine the inrush start with a "direct on line starter circuit" as used in motor control because they get mains fails from lightning etc.

Regards
M. Gregg

_________________
What is the sound of one hand clapping?


Top
 Profile  
 
PostPosted: 11 May 2017, 13:11 
Offline
User avatar

Joined: 08 Aug 2009, 03:11
Posts: 2225
Location: Chilliwack, BC
M. Gregg wrote:
The good thing about the timed resistor surge protector, is that at each start you get a guaranteed resistance at every start.


Yes.

In the case of an inrush limiter, if the unit if clicked "off", then "on" again, you get full surce as the ICL hasn't had time to cool down.

Also, the relay method can be used on the HV side of the transformer with correct relay choice, like an Omron G5NB series. Especially useful on some of these Japanese DIY designs I've seen that have half-a-farad of capacitance after the 350V rectifier :hot:

But in most other cases, an ICL is fine.

Cheers!

_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


Top
 Profile  
 
PostPosted: 15 May 2017, 10:51 
Offline

Joined: 29 Jun 2016, 15:59
Posts: 41
Guys,

Thanks for the replies.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 11 posts ]  Go to page 1, 2  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 19 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
DIY Tube Projects :: DIY Tube Amp Kits :: DIY Speaker Projects :: DIY Solid State Projects :: DIY IC / Op-amp Projects :: DIY Phono Projects :: DIY Cable Projects :: Hi-Fi Audio Schematics
© diyAudioProjects.com - Terms of Service - Privacy Policy