Differences between S.E.T & Push Pull Tube Amps?

[tube fanatic]

Yes, the output tube and the transformer to which it is connected will, to some degree, determine the amp's sonic characteristics.  Equally important is the operating point chosen for the tube (remember that they can be used over a very varied range of voltage, current, and load impedance).  Some operating conditions may result in more or less distortion which is often audible.  The power transformer's sole function is to deliver the voltage and current needed to satisfy a specific operating condition.  It does not in any way affect the sound of the amp as long as it is correctly chosen.  

 

The tube, and the load impedance into which it is operated, will determine the amount of power available.  Again, the power transformer has to be chosen accordingly.

The 300b amp you linked has deficiencies.  Among them are an inadequately filtered dc supply for the 300b filament, no bleeder on the p/s filter to ensure a full discharge of the caps, and a presumably non-polarized power cord (only a 3 wire cord should be used with the fuse in series with the hot lead, and the safety ground connected to the chassis and the amp's ground buss).  That forum has another 300b design (using a regulated dc filament supply) which looks much better, but even that doesn't have the bleeder (at a quick glance- correct me if I missed it).

 

I'd be concerned about doing such a build as a first project.  If your body gets between the 800V power xfmr secondary and ground you will not get a second chance at building another amp!  I'd go for something which runs on a much lower voltage (although that can kill you just as easily if things go wrong) until you get some good experience.

 

 

Maynard

[DaMuffinMan]

Thanks for the reply Maynard, and I will heed yours and everyone else s warning regarding voltage. I only want to build one of these so I want to do it right. I realize now with what I want to accomplish with this project that it is going to be closer to $1,000.00 by the time I get done, but that is OK.

 

Having said what you said regarding " 300b amp you linked has deficiencies" Is there another DIY project that can do the following. And not have any of the above mentioned concerns?

 

> 8 Watts

< $1,000.00 S.E.T. Integrated

Tone / Bass Control

2 Inputs   Is the 300B Tube the tube I should be looking at for what I want to accomplish?   Will these Output transformers perform for what I need? Magnequest RH-80 Hammond 1640SEA Edcor CXSE25-5K one electron UBT-2 Electra Print (custom ordered very $$) And I was also looking at this one Transcendar   How are Tone and Bass controlled in a tube amp?   Is it possible to integrate a phono pre-amp into a tube amp? Meaning not a separate pre-amp but part of the S.E.T. amp.       Thanks again everyone!

[tube fanatic]

My parts order delivery got delayed until tomorrow so I have a couple of minutes to spend on here!

 

If you want around 8W from a SET, the 300B is probably the best choice.  As to the price point, you may be close.  With modern 300Bs going for at least $100 each, combined with the cost of quality opts being in the range of $125-150 each minimum, there's not a huge amount left over with which to buy quality sockets, caps, enclosure, and so on.  You would have to run up a list and see exactly where you stand including shipping costs and possibly sales tax.  

 

Tone control is not typically included in modern designs although, admittedly, I do include a means of adjusting the high frequency response in all of my amps.  As to bass control, the only truly feasible way to employ that is with negative feedback. The latter is not normally used in triode amplifiers, and in SETs I consider it unnecessary as they offer more than enough bottom end.  Two inputs is no big deal. Same for it being an integrated amp.  

 

The impedance of the Magnequest, Hammond, and One Electron opts you mentioned is different from that specified in the schematic you linked above.  Using a higher impedance is not a problem with SETs as it will reduce distortion, but at the cost of some power output.  You also need to consider the dc resistance of the primaries as that will affect the resulting plate voltage.  Power supply values may have to be adjusted accordingly.   I have exclusively used Hammond xfmrs for so long that I can't comment on any of the others.  The appropriate Hammond for the schematic is the 1630SEA.  In my opinion, the Hammond opts are excellent in every respect.  

 

Yes, you can add a phono stage to any diy amp, but keep in mind that it needs to be very carefully designed if you are to avoid all kinds of hum and noise issues.  

 

So, that's the scoop.  If you are truly going to pursue building a 300B amp, do lots of research online for a design that has earned lots of praise from multiple builders.  Post the schematics and other info on here and I, as well as others, can give you our thoughts about it.

Maynard
 

[DaMuffinMan]

Thanks for the replies Maynard, will do.

 

How does this SE 300B stack up?   KISS

 

[tube fanatic]

1 hour ago, DaMuffinMan said:

Thanks for the replies Maynard, will do.

 

How does this SE 300B stack up?   KISS

 

Interesting design with its atypical method of biasing the driver and using SS rectifiers in combination with the tube.  Like the other 300b amps, you will be working with some very nasty voltages and won't get a second chance if you become a path to ground.  So, exercise extreme caution if you go ahead with a build.  Definitely research some sites which show how to lay out an amplifier chassis so you don't encounter any problems.  Routing of leads in this one will be even more critical because of the AC filament supply for the 300b.  

 

Maynard

[tube fanatic]

I came across this video which outlines some of the basics for laying out an amp chassis.  Although geared for a guitar amp, the same rules apply to any audio amplifier:

 

https://www.youtube.com/watch?v=XSkd9ymusNc

 

Maynard

[DaMuffinMan]

Thanks Maynard every little bit helps. I wanted to use aluminum for the base to mount everything on, now I know why to use it. Would it be ok to use a piece that is say an 1/8 inch thick for this?

[DaMuffinMan]

 Here are some other questions. Your thoughts are valued and appreciated.

 

What are your thoughts on the following statements?

" I would never recommend a 6SN7 as driver for a 300B".

 

 

and this one,"  I would not recommend a two stage approach".  

 

"Therefore, for me a three stage approach is best; it allows you the freedom of choice in terms of tubes and topographies. And the use of a passive volume control like a TVC or autoformer which hands down beats all active preamps, period. "

 

Should these be my "goals" for what i want to accomplish?

1.Separate PS for driver
2.Fixed bias
3.AC heating
4.Valve rectification
5.Useful to get power tx with heater windings and fixed bias windings.

And last but not least what does "nfb " stand for?

 

THANKS

[tube fanatic]

All of your questions fall into the category of "design philosophy " and everyone, including me, believes that their design is the best (of course, in my case it's the truth!).  So, you need to do as much research as possible and build based on what is most appealing to you and the budget you have.  There's been a huge amount of discussion about this on many forums like DIY Audio:

 

http://www.diyaudio.com/forums/tubes-valves/140771-best-300b-amp-schematics.html

 

http://www.diyaudio.com/forums/tubes-valves/79680-can-anyone-suggest-best-300b-se-sound-quality-schematic-beginner-like-me.html

It may also be useful to send a PM to forum member Erik2A3 as I believe he has more experience with the 300B than anyone else on here, especially when used with Klipsch speakers.

Nfb is an abbreviation for negative feedback which is used to reduce distortion and increase bandwidth.  It is typically used in pentode based amps as they often put out higher amounts of unpleasant distortion than their triode counterparts.

 

You also asked about using a chassis which is 1/8 inch thick.  That's certainly fine if you don't mind the effort involved in drilling through such thickness (if you have a press it is not an issue).  In most applications, it is not necessary to go that thick and even 51 mils is plenty for all but the heaviest xfmrs.

Maynard
 

[mike stehr]

One guy in the second link that Maynard provided mentioned a good simple driver circuit that can be used for 300B, or 2A3/45 as well.

SRPP, shunt regulated push pull, using a 6SL7. Should be enough voltage swing for a 300B grid...I know it's plenty for 71A.

 

There is so many schematics of home brew creations, variations of older circuits, (like the Loftin-White and Western Electric) using 300B that a guy can pull out his hair trying to figure which circuit to try.

My concern would be the 5 volt filament voltage required for 300B. Heating with 5 volts AC will require extreme attention to filament wiring layout. If attention to the wiring isn't taken, the amplifier will have filament growl through the speakers. And if they are high efficiency speakers like older heritage Klipsch, that filament growl will be even more accentuated. 1-2 millivolts could be acceptable...beyond that...no...

If I were using another DHT in the 5 volt range with regard to filament voltage, I'd would be thinking of heating the filaments with DC.

But there is also arguments about the effects of DC heating on a filament of a directly heated triode...something to the regard of filament sag or some such over time.

 

That's why I tend to favor the 2.5 volt heated triodes like 2A3 or 45. 2.5 volts AC is a bit more easier to tame with respect to filament layout/wiring.

You read these threads on DIY audio and it's more or less what flavor of driver circuit or output transformer to use. And really, that's what it kind of boils down to. Now you understand why some do it yerselfers resort to the bread-board.

[DaMuffinMan]

Thanks for the feed back.

[mike stehr]

Roust up your parts before you determine what size you want that 1/8" aluminum base to be...don't make it too small.

[DaMuffinMan]

OK Maynard I am going to listen to you and others advice and start out with a "safer" build.

What I would like to build is a tube amp set or pp you tell me. To drive a pair of Cerwin Vega 5-W bookshelf speakers. They are rated at 89 db. Here is a link to the dpecs. http://www.hifiengine.com/manual_library/cerwin-vega/v-5m.shtml

I will use this as a desktop system at work, speakers will be right in front of me. (2 feet) away.

This will also be a learning time for me b4 I tackle the FRANKENSET300B for my Cornwalls.

So if anyone has an idea of what I should build let me know.

Sent from my SM-N910T3 using Tapatalk

[tube fanatic]

Considering that even 1/4 wpc will let you part your hair (assuming you aren't missing most of it like me!) with the C-Vs at 2 feet, your options are almost limitless.  So, the only decision is whether you want to go with a kit or do a total scratch build.  If the former, the Bottlehead kit I linked on the previous page is nice in that there's a forum on which you can get all of your questions answered as well as learn about modifications, etc.  But, if you are determined to build something totally on your own, check out some of the amps I've featured on the forum.  All work extremely well with Cornwalls and should be fine with the C-Vs as well.  And, regardless of which way you decide, be sure to check out the numerous online articles and videos on electrical safety like this one before doing anything:

 

http://www.aikenamps.com/index.php/safety-tips-for-working-on-tube-amplifiers

 

Lastly, if you do a total diy project, consider posting a build thread on here as you proceed.  I'll try to help you if time permits, but I'm sure that William, Mike, and the other builders will try to do the same if they have time.

 

Maynard

[DaMuffinMan]

Maynard thanks for your replies (checks in the mail) and for the safety link (I do have all my hair, it's not going anywhere for a long time). I will review and also still looking for someone local that can give me some hands on help.

 

Yes I do want to build it from total scratch.

 

I will review your builds, I have seen the following, are there more?

 

The little Smoothie

The little Tater

 

[tube fanatic]

I presume you will be driving the amp from the computer sound card when using it with the C-Vs.  Before giving you a definite recommendation I need to know its output voltage (unless you are using an external DAC which should have more than enough output- but if you are using one, please post the specs so we can be certain).  Assuming that sufficient drive voltage is available, either of these amps would be my recommendation:

 

https://community.klipsch.com/index.php?/topic/161815-the-ultimate-gem-sep-is-here/

 

https://community.klipsch.com/index.php?/topic/159805-the-long-awaited-little-sweetie-mono-sets/&

 

Quite frankly, once you hear either of the above with your CWs I doubt that you will have much desire to go after a different build unless you want enough power to shatter glass.  Given the type of music you mentioned enjoying, the Ultimate Gem may be the better alternative if you want to build only one.  But, these amps are so inexpensive to construct (the total parts cost if you build both is below your budget) you may want to give yourself the option of enjoying SEP and SET sound.

 

In either case, finding an experienced local mentor is absolutely worthwhile.  I believe I previously suggested finding a ham radio or antique radio club as its members (especially the latter) should include many folks who are well versed in tube electronics circuits, and have the knowledge to work with high voltages safely.

 

Maynard

[DaMuffinMan]

Thanks for the reply Maynard!

 

I will be using it at work with my cell phone.

 

I am going to build the Ultimate Gem. I think I might gave found a few local ham radio clubs to go check out.

 

 

 

Are there some electronic tools I need other than a soldering iron & multi meter?

And is it better to buy a big kit of various caps or just what you need for 1 build?

[DaMuffinMan]

One other question, does anyone sell a diy tube kit with all of the electronic parts included and you build your own base? That is reasonably priced? So far the parts from the Lil Tater, Smoothie and Gem look about like 2-3 hundred in parts if I am off let me know.

[tube fanatic]

The best thing to do before getting involved with even a kit build is to purchase a bag of cheap resistors, capacitors, and terminal strips (look around on Ebay).  Mount the strips on a piece of wood and practice soldering the leads of the components until you get really proficient.  There are many video tutorials online on soldering technique.  It's important to become highly skilled in doing this as excessive heat can destroy a component.

 

If it were my choice, I'd go with the Bottlehead kit I recommended.  Yes, it's a bit more expensive than building from scratch, but has the advantage of a pre-drilled plate, with components properly located, to ensure correct operation.  And, as mentioned, you have access to a forum with dozens of guys who can guide you through the build process.  William is absolutely correct in advising you to go that route as an initial build.  Although the kit includes a wood base, you can certainly make your own if you choose and simply mount the amp plate on it.  

 

As to tools, even for a kit, you will need a small flush-cut diagonal cutter, needlenose pliers, various screw drivers, nut drivers, wire stripper, and so on.  Take a look at Jensen Tools' site and look at the electronics tool kits they sell.  Those are ridiculously expensive but will give you an idea of the various tools which are needed. You can then look for the best deal.  

 

Getting back to a scratch build, it is best to buy the specific parts needed for the project you are working on.  Parts kits rarely have the exact values required. And you will need the help of someone experienced to select the appropriate parts and where to obtain them. There's an antique radio repair guy about an hour from you in Clermont.  If you are still determined to start out with a total diy project (you need to have good skills with a drill to do the chassis preparation), I'd give him a call and ask if he can offer assistance.  If not, perhaps he has a friend or acquaintance who is available to help you out.

 

http://www.flradiodoc.com/

Maynard

[DaMuffinMan]

 

I will also be using my desktop pc (Realtek ALC887) is the motherboard sound chip will this work.

 

Here is the voltage information on the Audio portion of the Motherboard.

Full-Scale Output Voltage                                         Min     Typical     Max      Units
DAC                                                                           -           1.2          -           Vrms           
Headphone Amplifier Output@32Ω Load                  -           1.2          -           Vrms

Not sure if that is what you were looking for or not. Will I be able to play music from my phone?

 

That's funny that you recommended Mark, I emailed him and got a reply from him yesterday

 

The reason I was asking about the diy kits is because I was getting frustrated trying to figure out what all the parts are on your (and others) schematics.

 

But I am going to persevere and keep reading and asking questions.

 

On the Ultimate Gem schematic, are the following assumptions correct?

 

R1 R2 R3 etc. are these Resistors?

C1 C2 C3 etc. are the Capacitors?

RS407L  is this a Bridge  Rectifier?

Thanks everyone, have a Happy and SAFE New Year!