Output Power Question

[milsman2]

I appreciate all the ideas and after sifting through it all I kinda have settled on the K-502.

1.) Lots and lots of support threads that I have found to be easy to read and are very consistent with one another
2.) Relatively low price
3.) If I mod the OPT (1609 from Hammond) and get some orange drops or auricaps and leave out the DC blocking caps I've got an instantly way better amp
4.) It's my first build and I don't want to go too crazy
5.) I'll save the dynaco for next go around
6.) I'm ordering Klipsch RB-61's which should last me a lifetime of tube amp building

Last but not least, if I don't stop and order soon I'll have dozens of posts and no build

 

[rmyauck]

Because of this thread (read Poinz's comments as he builds amps for sale and knows his parts) you may want to consider others than Hammond such as the Edcor 10K with multiple outputs. Could be used in your later future EL84 PP amp as some commercial amps used close to that primary imp. Hammonds cost close to that Edcor.

EDCOR Electronics Corporation. CXPP30-MS-10K More info:

http://www.diyaudio.com/forums/tubes-valves/147313-k-502-upgrading-opts-hammonds.html

6V6 Amp Audio Circuit; Parts Expo Lots of good info from him too.

The K-502 probably uses output transformers like these as they do say they are made in the US.

EDCOR Electronics Corporation. XPP15-16-10K

 

[rmyauck]

Actually all the transformers used in the K-501 are Hammond, as if you look at the picture of the amp you can see the Logo! Probably K-502 ones are too.

 

[milsman2]

So is there really no point in upgrading the OPT's on the 502? This is assuming I don't want to build two 501's. Also, what about upgrading the hell out of the PS transfo on the 502? Part of my worry is upgrading the parts on the 501 x 2 as well as twice the initial cost = more than upgrading the parts on the 502 to get what could be considered really good sound.

 

[milsman2]

Update: I'm going to go with dual monoblock K-501's. They have Hammond PS and OPT already and I will have plenty more tranfo overall. Any suggestions for a pot to run this bad boy? Also, do I still need to replace the caps?

 

[aardvarkash10]

you don't NEED to replace anything. If you are going monobloc, you get to run side-by-side comparison so you can build to spec, then tweak away one one unit only until you get to where you want to be...

 

[milsman2]

Well lots of people on various threads have felt the need to change out the caps. I was just curious if this would be a great help or not worth it. Do you have any attenuator suggestions?

 

[aardvarkash10]

why does it matter?

Caps are a fetish for some - they may make a difference, but there are plenty of places to go first.

Attenuator? If you are really hung up on it go for a 20 position stepped unit with 1% Vishay resistors and a silver contact make before break switch. Otherwise, hang a half-way decent $10 pot in the space and let 'er rip.

 

[milsman2]

Fair enough as well. However, I want these to have one pot to control the whole stereo. Thoughts on the most efficient attenuators in terms of money vs. performance? This will most likely be the only initial mod. Specific models would be most helpful.

 

[aardvarkash10]

so don't put an attenuator in the amps at all. Make it an external. That way, you can change it without messing your chassis, and its in one place feeding your two 'blocs.

Moreover, you can be BUILDING THE DAMN AMPS and worry about the volume control later...

Sorry - losing it a bit over here....

 

[milsman2]

You got it chief. . I'll be ordering in the next few days...

P.S. Thanks for the push to actually build.

 

[aardvarkash10]

I recognise a kindred spirit...

 

[rmyauck]

I should mention for a future build you might favor the Tubelab PP EL-84 which I instinctively mentioned first after spending many, many hrs. reading the forms for the past almost 3 yrs. Great design and support and you seemed to favor PCB. I forgot to mention the 12AX7 is disdained by a number of amp builders/designers for it's sonics. Not as universally hated as the 12AU7 probably because the 12AX7 is used everywhere in vintage and new amps so not many have got to experience anything else including myself. The 7247 even contains both those tubes. The 12AU7 does seem to be okay according to some in the right situation. The 12AU7 can easily sub'd for others, without design changes, but not the 12AX7. Maybe it's octal equivalent the 6SL7 would be better in some situations. The 12AT7 looks like it has a few easy subs for tube rollers too. It seems everybody hears differently so I guess you have to try different ideas.

 

[JoeDJ]

Here's a simple table assuming a stereo amplifier and a speaker efficiency of 90dB.
Code:
Amp Power per channel SPL (dB)
1 W 93dB
5 W 100dB
10 W 103dB
50 W 110dB
100W 113dB
200W 116dB
400W 119dB

So clearly there is a point of diminished returns where big power amp really doesn't buy you that much more volume.

Yes, there are definate "diminished returns"
That is exactly why ample amp wattage is important.
Also let's not forget that different freqs can "demand" varying amounts of watts. so, any "table" is just a very rough estimate.

 

[milsman2]

Fair enough. I'm ordering the two K-501's soon and will build stock and just run it from a headphone to RCA jack cord. However, is anyone else concerned with the lack of EMI filter off the mains power cord as well as the lack of a 3 prong cord which could easily be grounded to the tranfo frame? The EL84's I will save for another day. Someone on my other thread has raised the question of the K-501's using 11MS8 tubes. Problem?

 

[boywonder]

Safety first.......

Use a grounded power cord and tie the ground wire to the chassis.......oh, and don't forget bleeder resistors on the PS caps (they may be included, I'm not familiar with the kit).

I have mains filters in all of my projects but I have not done a listening comparison with them and without. They are all surplus filters from my day job.

 

[Soonerorlater]

However, is anyone else concerned with the lack of EMI filter off the mains power cord as well as the lack of a 3 prong cord which could easily be grounded to the tranfo frame?

Needing an EMI filter is very much dependent on how " dirty " your local power supplies is. Filters/conditioners/ surge protectors are a lot cheaper these days and I've seen them built into 4 way gangs which can power all your HiFi. Over here in Europe it is becoming common to have them built into eurosockets.

The proper safety grounding of any amp is important and deserves its own thread. Our sticky thread on Safety Practices is a rewarding start for anyone who hasn't read it already.

Boy Wonder - no bleeder resistors - another mod.........

 

[Wavebourn]

EMI filters are needed if your device generates some garbage. But if it is a fair tube amp it picks up garbage from power outlet throwing it to your ground. Avoid EMI filters in your gear with analog power supplies.
Safety ground must be used. If ground loop is still a problem use transformer balanced ins and outs.

 

[milsman2]

So wavebourn, 3 prong wire but no EMI filter? Also, what are everyone's opinions on the stock tubes for the K-501?

 

[rmyauck]

11MS8- I never notice that either!

Googled those 11MS8 tubes and seems the are TV tubes. Lots of info such as:

http://www.diyaudio.com/forums/tube...-12m-11ms8-8-wpc-pp-tube-amp-kit-139-a-5.html


Kind of runs them hot etc. they say so maybe Stereo 502 has advantages you want?



Here's something simple that may be worth a look to you and would fit a "Starving Student's Budget" and is so simple you don't need a PCB. There was something similar with one EL84 a while ago on this form with LED bias which could be done with this one as a future mod. I bet it sounds really nice! You would have to build a high gain linestage though, but you don't need any coupling caps in the signal path! Should work with your 95/db speakers.

Tube CAD Journal: Tube balanced phono stage, July 1999

I wanted the smile with the one stage amp! How do you position them?