45 Type Push/Pull Amps

[jcmusic]

Originally Posted by tubelab.com

No you probably aren't. I have some scope plots somewhere on my hard drive showing over 20 volts peak to peak of unclipped bass guitar across my 8 ohm speaker. This is coming from my 45 powered SET. Do you believe that my 45's are really cranking out 6.3 watts? The plots are real, how is this possible? The answer lies in the fact that "8 ohm" speakers are rarely 8 ohms, and will go quite high in the low bass region near resonance. My speakers are about 20 ohms in the range I was testing, which works out to a little over 2 watts.

I have a little 45 SET. I run the 45's (or my favorite NX-483's) at 325 volts and 30 mA. The extra plate voltage allows headroom for the average speaker in the bass region. The NX-483's were made before 1929, have been in the amp for almost 10 years and still work great. My amp has been auditioned along side some high dollar equipment and stands its ground quite well, and is often favored by some listeners, especially in the dynamics department. OH, yeah, the power supply uses a $40 transformer, probably has several hundred ohms of DCR but there is a low ESR motor run cap right at the red wire on the OPT. The secret to dynamics is the ability to run right into A2 without distortion and total freedom from overload and recovery issues. AND...I can hold the amp in one hand. I don't have room for huge amps.

BUT, this thread was about push pull 45 amps. I have built a few, but currently don't have a working 45 push pull amp. Why? Tubes. I have about 20 45 tubes. All are quite well used, and most were obtained for $10 each or less. A pair of 45's in class AB2 push pull can deliver 18 watts according to the data sheet. To do this the tube MUST have ample reserve emission capability or the dynamics will suffer and the amp just won't come alive. Most of my well worn tubes will work fine in class A1 or A2 even in push pull, but can't pass the 100 milliamp peaks needed for AB1 or even more for AB2.

I had a fully differential (3 cascaded LTP stages 6SN7's ---> 6SN7's ---> 45's) push pull amp running for a while. With a CCS in the tail of each LTP it MUST run in class A, and roduced about 4.5 watts on 325 volts. It sounded excellent, but I swapped the 45's for triode wired 307A's, raised the B+ to 375 volts, changed taps on the OPT's (UTC LS-57's), and got a great sounding 15 watts.

(NO YOU PROBABLY AREN'T)
Dude that's pretty bold of you to come into this thread and make a statement like that without knowing anything other than what you have read!!! Enough said!!!

[ErikdeBest]

I may be criticized for this, but I really dislike the way this thread is going:

1 - JCMUSIC is not being clear on his problem: 106dB sensitivity, listening between 86 and 89dB, and saying 2W is not enough, and then attacking George (tubelab).
2 - other newcomer talking about 'thinking ouf of the box', and that just against Thomas (Vinylsavor) who's showing lots of 'thinking out of the box', on, for example, his blog.

I know both George and Thomas can defend themselves, but when I see this sort of newcomers coming, asking for help and then ignore advice, I am afraid people like George and Thomas will just slowly walk away from this forum, and I would hate if that would happen.

best regards, Erik

[jcmusic]

Originally Posted by ErikdeBest

I may be criticized for this, but I really dislike the way this thread is going:

1 - JCMUSIC is not being clear on his problem: 106dB sensitivity, listening between 86 and 89dB, and saying 2W is not enough, and then attacking George (tubelab).
2 - other newcomer talking about 'thinking ouf of the box', and that just against Thomas (Vinylsavor) who's showing lots of 'thinking out of the box', on, for example, his blog.

1 - JCMUSIC is not being clear on his problem: 106dB sensitivity, listening between 86 and 89dB, and saying 2W is not enough, and then attacking George (tubelab).
but when I see this sort of newcomers coming, asking for help and then ignore advice, I am afraid people like George and Thomas will just slowly walk away from this forum, and I would hate if that would happen.

best regards, Erik

1 - JCMUSIC is not being clear on his problem: 106dB sensitivity, listening between 86 and 89dB, and saying 2W is not enough, and then attacking George (tubelab).
Listen up dude!!! I never said I had a problem, I never said that I listen between 86-89db read closer and know what you are saying before getting in this thread and making claims.

2 - If George and Vinylsavor feel attacked they can defend themselves you on the other hand should be more concerned about YOU and not others...

[wicked1]

Man! Respect!
These guys you are arguing w/ have been here helping people for many many years.
Looking back at your post history, you have not! You need to sit back and happily take peoples suggestions, whether you agree w/ them or not. Complain to yourself at your computer desk, but don't start arguments here. Everyone is here for learning and help.. keep the attitude elsewhere.

(-maybe a mod could delete this and the past 3 posts)

[jdg123]

I must apologize for the roll I play in a bit of this confusion. I asserted that jcmusic and I have similar listen levels and put my OWN at 86 - 89 dB. His listening level assessment was 86 -95dB. At 95dB operational parameters are quite different! Sorry all.

[jcmusic]

Originally Posted by wicked1

Man! Respect!
These guys you are arguing w/ have been here helping people for many many years.
Looking back at your post history, you have not! You need to sit back and happily take peoples suggestions, whether you agree w/ them or not. Complain to yourself at your computer desk, but don't start arguments here. Everyone is here for learning and help.. keep the attitude elsewhere.

(-maybe a mod could delete this and the past 3 posts)

Here we go now another unnessacary comment from someone who has not contributed one iota to this thread!!! I am not going to get into this with you mind your own affairs or else kick rocks!!!

[jcmusic]

Originally Posted by jdg123

I must apologize for the roll I play in a bit of this confusion. I asserted that jcmusic and I have similar listen levels and put my OWN at 86 - 89 dB. His listening level assessment was 86 -95dB. At 95dB operational parameters are quite different! Sorry all.

John,
No need to apologize if you read close enough this would have been obvious but, most just can't wait to insert their 2 cents and that's where the confusion comes in...

[iko]

Please move away from personal commentary and let's get back to the technical aspects. A word of advice to those who are new to this forum. Everybody's welcome here, however new or veteran. We expect everybody to be civil. We also value those who have contributed and helped so many users over the years. Let's be nice and try to understand the other people's point of view.

[tubelab.com]

I attempted to explain that simply connecting a scope across the speaker terminals and observing the voltage will not provide an accurate measure of the power actually being delivered to the speaker. Taking the speakers impedance VS frequency curve into account will remove the largest error, but there are still reactive and counter EMF errors. I had to learn this the hard way years ago.

I also attempted to demonstrate that not all 45's are suitable for class AB use.

If my explanation ruffled someones feathers, then I apologize for that. I now have very limited access to this forum (smartphone only) during the day now due to my day job's internet policy, so my posts have become infrequent. I will not be back to this thread.

[jcmusic]

Ok guys I am sorry if I was disrespectful to anyone here but, it bothers me when folks who have nothing to do with the current topic get involved just to be typing or voicing their opinions!!!
So I apologize to those I may have offended, and to those that tried to help or had something of value to contribute thank you very much...