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 15 Aug 2020, 08:45

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 755 posts ]  Go to page Previous  1 ... 72, 73, 74, 75, 76  Next
Author Message
PostPosted: 13 Jun 2020, 20:43 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4212
Location: Arizona, USA
Hi, Yes.... the important aspect of using the CCS is that the voltage on the cathodes is equal and the grid of the second tube is at ground potential. Thus it effectively sees the same drive voltage but in an opposite phase from the one that gets the actual signal. The variable resistor (some versions) in the cathode circuit allows for very close current balance between the tubes. Think of the arrangement as a see-saw. When one goes up the other has to drop by the same amount. The CCS enforces this mechanism. You can use other CCS, but IMO none work as well, reliably and cheaply as the LM317HV. Just keep the voltage across it over about 4 volts and it will be happy. Below that you get some really strange wave forms. With the small positive voltage on the grids this is effectively prevented. There are two variations of the balance method. One adjusts the positive voltage between the grids and the other does not. It uses a 25 ohm pot between the cathodes with the center tap going to the CCS. Both work well and sound the same. The one is a bit more elegant though and can deal with tubes that are less well matched. I suggest that folks use tubes that are close to the same for best performance. Matched pairs are the best. If the tubes are not well matched then the low level output will be fine...but as it increases there is the likelihood that they will not sync together and the higher the power gets it will distort more.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 14 Jul 2020, 14:44 
Offline
User avatar

Joined: 14 Sep 2014, 18:24
Posts: 3
Location: Santa Clara, California
PoddWatt Completion!
I wanted to share my completed PoddWatt with all and thank Bruce and everyone else for all the listed information that helped me complete it. One issue I wanted to get feedback on is everyone's experience with how much heat this amp produces. I have build tube guitar amps in the past and know that they get warm, but this amp's tubes seem to run extra hot. I've checked voltages and done bias checks and all seems within range. How hot does your build get? Thanks all!


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



Top
 Profile  
 
PostPosted: 14 Jul 2020, 21:33 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4212
Location: Arizona, USA
Hi, most guitar amps run in class AB. The tubes draw a fairly small amount of power at idle. The Poddwatt and indeed all the "Oddwatts" run in class A (for the highest quality sound) and as a result draw the maximum power at idle. So yes the tubes run on the hot side. Not excessively so as the dissipation is designed to be about 85% of max for good tube life, but still a lot hotter than in a guitar application where the idle load is about 40%.

EDIT: The build looks quite nice

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 19 Jul 2020, 12:12 
Offline
User avatar

Joined: 14 Sep 2014, 18:24
Posts: 3
Location: Santa Clara, California
Thank you Bruce for the information and kind words.

Question: I live in an older home where the wiring is the older two-wire 120 volt hot and neutral. I realize it would not be ideal, but is there a safe way to
wire the PoddWatt to work effectively without the earth ground?

Thanks!


Top
 Profile  
 
PostPosted: 19 Jul 2020, 13:18 
Offline

Joined: 02 Jun 2020, 08:56
Posts: 3
From a purely safety standpoint, the proper way to do it according to the NEC (National Electrical Code) is to replace your old two-prong outlet with an standard GFCI outlet. A GFCI does not need a ground to operate. Instead, they make sure that the current coming out of the hot wire matches the current going back into the neutral. If the power leaks out anywhere else, the breaker trips. The GFCI will come with a sticker in the box that says "No Equipment Ground". Put that sticker on the face of the GFCI and you are good to go: it indicates precisely that the GFCI is ungrounded. The result is actually safer than a grounded outlet. Here is a link if you are interested: https://www.ecmweb.com/content/article/20896746/replacing-2wire-ungrounded-receptacles

I will defer to the experts to explain if you need an earth ground for sonic requirements.


Top
 Profile  
 
PostPosted: 19 Jul 2020, 18:39 
Offline
User avatar

Joined: 14 Sep 2014, 18:24
Posts: 3
Location: Santa Clara, California
Thank you very much for this information. I definitely should replace some of my two-prong outlets with GFCI ones as a short-term solution before rewiring the entire house. I was also wondering if there was something that could be done inside the amp to insure a hot and neutral connection would work. Is it possible to connect the neutral and earth within the chassis? Is there any potential problem with doing that? Thanks again!


Top
 Profile  
 
PostPosted: 19 Jul 2020, 20:31 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4212
Location: Arizona, USA
Hi, Yes a GFCI will work. I would consider building a multiple outlet junction box with the GFCI in it. Then run all the audio gear from it. That way if any of the gear needs external chassis grounds between the components it should work well. The issue with grounds between things is that they have several functions. A lot of gear (Oddwatt included) maintains a separation of earth (chassis) ground and signal grounds for reasons of low noise and safety. With only a two wire system the gear must (per most electrical codes) have all external metal parts double isolated from accidental contact. This can be done, but adds complexity and cost to gear. So if you want to say I take the easy way and earth ground the chassis, fine, it is true.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 31 Jul 2020, 10:42 
Offline

Joined: 29 Jul 2020, 12:26
Posts: 5
Hi, new here and looking forward to building this amplifier. A quick question, can I use 220nF capacitors in place of the four 330nF as I already have some quality ones to hand from another valve project? Many thanks.


Top
 Profile  
 
PostPosted: 02 Aug 2020, 11:36 
Offline
Project Author
User avatar

Joined: 04 Jun 2008, 20:59
Posts: 4212
Location: Arizona, USA
Hi, It should be fine, the rolloff will be about 14-16HZ with .33s it is closer to 8-10HZ. In the real world unlikely to be noticed as there is really little content below 50HZ.

Good listening
Bruce

_________________
Some of my DIY Tube Amplifier Projects:


Top
 Profile  
 
PostPosted: 02 Aug 2020, 13:46 
Offline

Joined: 29 Jul 2020, 12:26
Posts: 5
Thanks Bruce. As the designer, what in your opinion is the definitive stereo version with a single PSU, is it the one with the three LR8s, or just the two, and is the OP transformer wiring identification now sorted? Cheers, Richard.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 755 posts ]  Go to page Previous  1 ... 72, 73, 74, 75, 76  Next

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: Majestic-12 [Bot] and 18 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