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Old 6th July 2006, 05:45 AM   #1
CLS is offline CLS  Taiwan
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Default SE for Bass?

Hi there,

I made a little 6C45 single stage SE amp the other day. It runs on about 186V on anode, 2V LED on cathode, sounds very good with airy openness & loads of details...

This flea amp is fed by an active xover, serves from 160Hz & up.

For the other end, below 160Hz, I've tried 300B SE (which was originally at the position of 6C45 SE now)

Mid to high from 6C45 is very good, despite the tiny power under 1w. However, 300B on bass somewhat disappoints me


My 300B amp is so-called DRD circuit, with the same 6C45 as driver loaded by choke & direct couples to 300B. 2 power supplies with individual LCLC, and the output is stacked on the driver. The 300B sees 427V on anode & 71V on cathode with 76mA DC current.


Bass sound from this 300B amp is not all that bad, but sometimes it's too soft I should say.

Even jazz piano trio can make it exhausted. Sometimes, overlapped notes from acoustic bass & kick drum are smeared when they are fast enough. Usually that's when the rhythm getting hot, but with the smeared bass notes, the motivation of the music is lost It became a noisy chaos

However, sometimes the bass solo can be good, with crisp snaps & good pitch definition.

I think it's OK in the mid-bass range, but looses control on the low end...


I've read an article on <Sound Practices> several years back, about the gapped output trany on SE amps. It says, SE amp can actually do better than PP on the bass region, unlike most people might think. That's because the gapped output trany is very linear so the low level details are well kept. This contributes to good bass response.

In my recent experience on this, I doubt.


Before this, I used a pair of antique Altec 1568A for bass. They were modified with 2 pairs of big chokes & more caps. And the original 6CA7 output tubes were swapped to 6L6GC. This amp is good on bass, at least better then 300B SE.

Before Altec, I used a sand amp, a good (& hot) one-- Kinergetics KBA75. It's, simply put, rock-solid. No wonder, it's a "solid" state amp...


Why don't I go back to sand? Maybe it's some kind of obsession with tubes... (and now, not only tube, but low watt and SE... )



Soooo....., what's next? Keep trying to squeeze out more potential from 300B? (until I kill it? I think I've been very close.)

Or, I got several 811A & SV-811-3 which can take high voltage or be driven into A2 to get bigger output.
( But, does more watt really means good bass? )

Or, I should try low-z tubes? I got several 6336....

Or, I should totally forget about SE for bass....


Any thoughts?
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Old 6th July 2006, 07:06 AM   #2
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Bass amps and SE can work well, but you have to be bold. Unlearn what you have learned from HiFi (and put the 300B in the power supply )

Breadboard this: 6L6GC SET and drive it with something insane, like a 6CB6. Listen to it (yeah 1 watt, but listen ) Quite the tonal quality and thump, eh? Now just find a more powerful tube.... transmitting tubes are good and don't overlook triode connected horizontal sweep pentodes.



Good luck!
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Old 6th July 2006, 09:03 AM   #3
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Hi CLS,

bass response with SE amps usually is limited by core saturation effects of under-dimensioned OPTs.

However, there is no reason you cannot get, say, 15Hz flat (at -1dB) at 15 Watts Po, at 165mA iddle current, w/o any sign of iron hysteresis, from say, a triple of paralleled triode strapped EL34 or something. Been there, done that. The problem is, you will need a core size of about EI126 with about 1,5-2kg of copper (for each OPT, of course).

Tom
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Old 6th July 2006, 01:44 PM   #4
Sherman is offline Sherman  United States
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A KT88 running SE UL driven by a 6N1P with an OPT of 5K (I'm using James 6123HS) produces very good bass.

Search this forum for Mikael Abdellah's SE KT88 for the schematic.
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Old 7th July 2006, 07:03 PM   #5
Jeb-D. is offline Jeb-D.  United States
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Quote:
Bass amps and SE can work well, but you have to be bold. Unlearn what you have learned from HiFi (and put the 300B in the power supply )


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Old 7th July 2006, 07:30 PM   #6
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Quote:
A KT88 running SE UL driven by a 6N1P with an OPT of 5K (I'm using James 6123HS) produces very good bass.
Search this forum for Mikael Abdellah's SE KT88 for the schematic.
Still my best tube amp
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Old 7th July 2006, 10:57 PM   #7
Sherman is offline Sherman  United States
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Quote:
Originally posted by Simpleton


Still my best tube amp

I still love mine as well!

Because I can't leave well enough alone I'm thinking of replacing the 6N1P cathode resistor with a LM317-based CCS. I have a bunch of LM317s in my parts bin so the modification will cost me a resistor! I'll report back when I finally get around to soldering it in.
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Old 16th July 2006, 03:11 PM   #8
SET12 is offline SET12  United States
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Geek,

This is my first post here on DIY I have been a member for some time but your post really hit a stimulating nerve with the debut of PP vs SET and the issue of quality bass from a SET people are not thinking out of the box! by being bold for instance I use a very fast 200 Joule power supply for each one of my Monoblocks, I use a design that allows me to get the transparency of an all Polyprop based supply while using electrolytics for bulk I discovered this by looking to obtain speed in my supplys

Most people seem to make such an issue over going after noise and using really big chokes of high inductive values, when they should be doing just the opposite by using large cores with low inductive values which keeps the DCR low as well.

I once conducted a little experiment as you know many vintage push-pull amps used a 100 ohm resistor between the first cap that the rectifier uses and the second cap that feeds the output stage center taps.

The resulting music had a punch that was startling opening my eyes!!!

Tubes4e4,

You also hit it on the head! I use the Hammond 75 watt 5k SE for my 10 watt SET there surely is a greater sense of ease with with the larger core great space, supurb low end extension if fact my SET had no trouble at all beating out a Jollita 100 watt hybrid in virtually every area except in sheer volume the soundstage was also only half the size of my SET's alot of this I feel is contributed by the large core of the hammond I also realize that Hammond has not always lived up to their claims in their specs with the SE line but I can say the 75 watter is working for me!

SET12
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Old 16th July 2006, 04:14 PM   #9
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Hi SET12

Interesting point on the use of elco's...how did you compare both? Hvae you built a 200J supply and made AxB comparison? (Should be bij, 200J with poliprop..)

I think that noise is a big issue in SE designs...but you are using low inductance chokes, prefering low resistande in spite of the noise? Have you tried regulated supplies?

I don't understand what you did in your experiment...you talk about the resistor from 100R...but what did you do with it? Shorted, substituted for a choke (low DCR off course, otherwise it's bad).

I am curious - and all ears

Erik
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Old 16th July 2006, 04:57 PM   #10
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Quote:
You also hit it on the head! I use the Hammond 75 watt 5k SE for my 10 watt SET there surely is a greater sense of ease with with the larger core great space, supurb low end extension if fact my SET had no trouble at all beating out a Jollita 100 watt hybrid in virtually every area except in sheer volume the soundstage was also only half the size of my SET's alot of this I feel is contributed by the large core of the hammond I also realize that Hammond has not always lived up to their claims in their specs with the SE line but I can say the 75 watter is working for me!
Have you measured the high frequency response with this transformer? I need a big transformer for a big amp. I have asked on the forums before if anyone has any experience with them, and my questions went unanswered? I just got a pair of their 1628SE's and the response from 10 to 20KHz is poor.

Below that it is flat down to a -3db point at 14Hz. The bass is killer with a 10 watt SE amp in UL mode. I am also using a low impedance power supply with motor RUN caps for filtering. I can switch between SS and tube rectifers on the fly, and SS has better bass. A big toroidal power transformer and a 40 ohm choke help too.
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