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mike stehr

Maynard design 6AQ5/6005 SEPP amp w/James OPTs (impression/take)

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Okay, about a year or so ago I seen Maynard had posted this amplifier on the forum. It sparked my interest. Could this circuit with James OPTs have the nice sound using Cornwalls like ​my little SEP 6BQ5/EL84 amplifiers? Yet with a bit more power and bass grunt?

 

I have a pair of oak '83 Cornwalls, with K51 mid drivers, Crites CT125 tweeters, and Crites woofers. Crossover networks are charge-coupled B2 version, with Dayton Audio 1% tolerance polyprop caps.

 

I have always enjoyed single-ended tube amps with the Cornwalls, along with a Scott LK48B 7189 PP amplifier for listening to vinyl. I like the Scott's phono stage...

I've listened to 2A3, 45, pseudo 300B, and 6BQ5 tubes in single-ended amplifiers. I have a DHT 2A3 stereo amplifier that I enjoy with the Cornwalls. I also enjoy a SEP modded Magnavox 6BQ5 console amplifier, and a DIY RH84 amplifier.

I have a small living room, and listen to the Cornwalls in a semi near-field to near-field arrangement. I don't need that much power for moderate to loud levels.

 

The DHT 2A3 amplifier sounds excellent with most genres of music. Triodes like 2A3 have a bit of accentuation in the midrange...great for some music, but not for music like hard metal. The in your face guitar sound of this type of music can be overbearing with triodes.

However, with milder rock music, Jazz, Electronica, and rap can really sound good with the 2A3 amplifier.

 

Using the Magnavox SE 6BQ5 amp or the RH84, both amplifiers have feedback. (one from OPT to the first tube's cathode, and the other a type of Schade feedback)

These amplifiers don't have the accentuated midrange, and are less forgiving with hard rock and metal. And used within their operating parameters, they can sound rather nice and balanced on the Cornwalls.

 

I would listen to either amplifier with their small output transformers and ponder that it would be great to have this nice SEP sound, but with a bit more power and bass grunt like the 2A3 amp. Don't get me wrong, the little SEP 6BQ5 amps have good bass, it's just limited.

 

So I took a chance and went for Maynard's 6AQ5/6005 SEPP circuit...I started off as a breadboard project, and progressed to completed amp. The thread title is "Parallel 6AQ5/6005 SEP amp". I can't post the link for some lame reason...information about the build is in the thread.

 

There is about six hours of listening time with the amplifier so far. I'm using a Heart/Marantz tubed output CDP for a source, so this evaluation/review is based on CDs. I have a Raspberry Pi2 with HiFiBerry DAC using Kodi for a music server, but I haven't used it yet. I don't have a phono preamplifier for vinyl.

At initial power-up the amp sounded a little bright for about an hour or so, and then seemed to settle-in. (or my ears got used to it)

 

I played whatever I could as far as genres. Mancini's "Pink Panther" theme sounded amazing, with strong full bass. 2LiveCrew bumped bass like a car stereo, as it should. You can hear the scratches and noise on the records they used to dub with.

I played Nazareth and Rush "Moving Pictures". The track XYZ was impressive, punchy and tight for Cornwalls.

Meat Beat Manifesto is Electronica. (I think?)  There is deep low bass with this music, the 6AQ5 SEPP pulled it off excellent.

Brubeck's "Take Five" sounds wonderful.

 

I have been using the ear-bleed circuit, and it does help tame some harsh music. But I should swap out the 2200 picofarad polystyrene cap for a polyprop or polyester. I feel the effect would be more pronounced using the former dielectric types.

 

This amplifier gives the impression of real low bass, it seems you can hear earth noise...it's that deep. I'm pretty sure this amp has stronger bass being a little more power than the 2A3 amp. But I would have to compare the two amps to determine which gets lower in bass. It's real close. The 2A3 amplifier may have a bit more natural sounding bass/midrange compared to the 6AQ5 SEPP, but I wanted the SEP pentode sound (using some form of feedback) with a little more power and bass.

 

It's pretty much exactly what I wanted. I had never planned on going farther than bread-boarding with the project, but I'm glad I did make a completed amp.

 

Thank you for Maynard for your kind help and guidance. It's been a fun project, and look forward to another!

 

Mike

 

post-4542-0-57540000-1460268127_thumb.jp post-4542-0-63820000-1460268195_thumb.jp

 

post-4542-0-02420000-1460268335_thumb.jp post-4542-0-39540000-1460268454_thumb.jp

 

post-4542-0-50380000-1460268708_thumb.jp

Edited by mike stehr
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That is absolutely gorgeous Mike!  Your build quality is phenomenal!!!  Regarding the sound, William recently mentioned that he noticed a huge improvement in the sound of his "Sweeties" by switching over to Orange Drops for the coupling caps between the drivers and output tubes.  If you happen to have a pair around with the correct value, it may be interesting to try them and note any changes.  In any event, I'm glad that the amp met your expectations!!!

 

Maynard

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I would have to agree with Maynard,that is a beautiful build!

I want to thank you also for taking the time to post your impressions and pictures of the amp. I have gathered all the components to build the little sweeties and quality pictures like you have posted are a big help to a first timer.I realize the circuit is not the same but it still is of help as a general guide to layout.

If it sounds half as good as it looks, you will be smiling for some time to come!

Stacy

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That is absolutely gorgeous Mike!  Your build quality is phenomenal!!!  Regarding the sound, William recently mentioned that he noticed a huge improvement in the sound of his "Sweeties" by switching over to Orange Drops for the coupling caps between the drivers and output tubes.  If you happen to have a pair around with the correct value, it may be interesting to try them and note any changes.  In any event, I'm glad that the amp met your expectations!!!

 

Maynard

 

Thanks again!

 

What type of Orange Drop did he swap to? 715P, or 716P? I'm pretty sure both series are a metalized polypropelene, but the 716P has copper clad leads, where 715P had steel clad leads.

 

The little black Magnavox SEP 6BQ5 console amp I have now, uses the Russian military K40Y caps. My 2A3 amplifier uses the K40Y caps, as well. The RH84 DIY amp, uses Jensen aluminum film and foil caps. The little white Magnavox SEP 6BQ5 console amplifier I built has RT series RelCaps.

 

The RT series RelCap would be the coupling cap I would like to try with the 6AQ5 SEP. The combination of carbon comp, and carbon film resistors, along with the RelCaps made that little white Magnavox SEP 6BQ5 sound great.

But I've only seen 0.22uF, no 0.27uF.

 

Amtrans makes a polyester cap that looks interesting. I think the Leben guy used a variant of these. But only 0.22uF is produced.

I've used polyester caps for coupling in a 6BQ5 PP console amplifier, I don't have any issues with Polyester types.

I've used 716P in my Scott integrated amplifier. The 716P is a good cap...copper leads, a metal polyprop, and epoxy dipped...tough.

 

They make a 400V 0.27uF 716P according to CDE...it's just finding a vender that has that value in stock. Mouser doesn't have it, which is why you and I used Panasonic polyester 0.27uF 400v caps.

 

I found Mundorf M series 0.27uF 630 volt caps online from a vender. $5.50 a pop...not too bad a price I suppose...

They are a metal polypropolene.

 

Now you got me all cap tweeky...I could pony up and use RelCap 4700 picofarad 630v RTE series for the feedback HP RC network. Spendy little buggers...I'm using a CDE orange drop 715P series now for 4700pF.

 

The input cap is a 715P. I can swap that for 716P.

 

I'd rather use a 0.27uF 716P for the coupling caps due to the size, but the Mundorf may not be a bad choice.

The RT series RelCap would awesome, but no 0.27uF value.

 

Mike

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As the owner of one of these as well, that thing looks beautiful. What did it wind up on wattage? About 4 WPC?

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As the owner of one of these as well, that thing looks beautiful. What did it wind up on wattage? About 4 WPC?

 

I never actually measured the wattage per channel, but more than likely about 4 watts.

 

Maynard reworked your amplifier's power supply with larger value load resistors, to keep the power supply transformers within their current specifications. I had to follow along the same guideline. Instead of the sand cast resistors like Maynard used, I'm using 25 watt aluminum power resistors sinked right to the chassis.

 

The heat dissipation from the voltage drop across the resistor, (wattage) is well within spec, but it still warms that chassis up quite a bit.

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So a guy like me parks this amp in April/May...things warm up, it's summer other things go on.

 

Fall rolls around, audio projects come to mind.

 

Went through a Kenwood SS receiver so the GF can have tunes while I'm gone.

Found out about some modifications to a Magnavox console amplifier that had been shelved for years, so went and did the mods so I can have another working tube amplifier instead of another carcass.

Same with some mono 6V6PP Magnavox amps I have. They were just sitting around and I needed to follow through on the project.

 

So while I'm awaiting parts for a mono 6V6PP amp, I decided to dust off the Maynard 6AQ5/6005 SEPP amp and give a listen with the Cornwalls.

And then sit and wonder what the hell I've been doing these other projects for the last 3 months...

 

DSCN2461.JPG

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That is a nice looking amp.  Clean inner and simple which is excellent.  Rolling tubes can change the sound and make some music a bit harsher depending on the tube gain structure.  A out board EQ can remedy those fluctuations and cut down on the number of tube purchase in my  case.

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1 hour ago, derrickdj1 said:

That is a nice looking amp.  Clean inner and simple which is excellent.  Rolling tubes can change the sound and make some music a bit harsher depending on the tube gain structure.  A out board EQ can remedy those fluctuations and cut down on the number of tube purchase in my  case.

 

It's nice to not have to worry about some oddball tube rectifier, and the benefits of having more PS filtering. Though I like tube rectifiers, big half wave television damper tubes like 6AU4.

 

The amplifier has the Maynard "ear bleed" circuit. When switched on, you can adjust the top-end a bit with recordings that tend to be a bit overbearing on top.

 

Rolling tubes...I have three NOS red label GE 5 star 6005s in the amp, with a lone white label GE 5 star 6005/6095. (didn't get a fourth NOS 6005)

I have a good quad of Sylvania 6005 with the grey/shielded glass to try, and a good quad of RCA 6AQ5.

The RCA 6AQ5 are tubes I would like to roll in the amp to hear a difference. Otherwise, I'm good with the GE 6005s.

 

As far as the 6SF5, I could roll some different brands, maybe try some glass versions. Then again, there is some reasoning for using a metal tube, and I'm a RCA guy...

 

The amplifier also uses a type of HP network series RC feedback.(I think I got that right) 

Maynard brought up this type of feedback and formula, to coincide with the low frequency roll-off (F3?) of a Cornwall.

I recall 38Hz for a Cornwall, so we figured/adjusted the filter for around 40Hz. It almost works somewhat like a little boost to my ears.

 

Die Antwoord and old school rap just pound with this amplifier, no need for a subwoofer in my small near-field setting.

And I still have the beautiful midrange and top-end sound of tubes.

The James OPTs are no slouches. The only other amp that can do bass like this amp, is my 2A3 amp...and it's time fire it up and compare. The 2A3 amp will have a wee touch of filament growl, due to direct heating a filament with AC, so it didn't win in the idle quiet department. The 6AQ5/6005 SEPP amp is as quiet at idle as solid state...

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Your amp is a work of art Mike. Where are you getting the ceramic strips from?

 

 

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I would like to "bump" this thread,  in February 2019.

 

I have worked with 6AQ5 and 6005 amps, off and on, for the last eight years.

 

Here is what I have found necessary for highest performance, and what I prefer:

 

a) a directly-coupled amp, over any using a coupling cap, or interstage transformer

b) a two-stage amplifier only, over all amps with three stages

c) tube rectification, directly heated, 5U4GBs being one excellent choice

d) choke input filter, using dual series choke/cap sections, eg: L1/C1/L2/C2

e) I find it critically important, that chokes have a DCR of 10 Ohms or less, and it does not need to meet " critical inductance ", what-so-ever

f) triode connection of the 6AQ5/6005, even if it has less power

g) no capacitor larger than 50 uF, and all film caps, no electrolytics

h) Military Spec internal wiring, copper and silver plated, teflon jacketed.  The equivalent of 8 AWG for ground returns ( three wires in a bundle, paralleled )

i) conservative plate dissipation / operating points , typically about 62% of maximum ratings

j) no feedback 

 

A SE version of the above will only put out 0.25 Watts clean, and 0.33 Watts maximum, so it will NOT be good for a Klipsch speaker.  A Push-Pull version of this design will put out maybe 2 to 4 Watts, and be appropriate / superb for a similarly re-wired / well-wired Klipsch vintage corner horn.

 

In the coming next two months, I will design and prototype this, work out the values needed, and give it a whirl.  Two stage, P-P 6005s.  I love the 6005, it is a " firecracker " of a tube.  IMHO,  I find it totally and easily SMOKES any NOS Type 45 DHT Finals tube I tried. (  I have NOT used the $$$$$  EML s ).

 

Amps, not good speakers, in my own opinion, are the weakest link in high performance audio.

 

Have fun, I sure do.

 

Jeff

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29 minutes ago, Jeffrey D. Medwin said:

Amps, not good speakers, in my own opinion, are the weakest link in high performance audio.

Beg to disagree. PWK would. But I believe he'd also say that even with great speakers it's all about the source material...you can't fix crap.

Dave

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1 hour ago, Mallette said:

Beg to disagree. PWK would. But I believe he'd also say that even with great speakers it's all about the source material...you can't fix crap.

Dave

 

Hello Dave,

 

Wow, you are a moderator, so I have to be careful.  I disagree with you, however.

 

Now a days, source is no longer the problem.  In 2019, we have great turntables, wonderful tonearms, cartridges, and great High Rez digital capabilities. In PWK's time, this was absent.

 

The one quote I seem to recall from him was :

 

                    " What the world needs now is a GOOD five watt AMP. "   

 

It hasn't changed much at all in my opinion, I personally feel 99.9% of the amps in existence are highly deficient.  That is why I have been amateur designing and DIY building my own, for the last 40 years, precisely as outlined in my first post. 

 

Simple A-Bing of amps, full range, in a really GOOD High Efficiency system, could easily prove my point.    Alas Dave, you likely live far away from Kansas City, MO !!

 

You have a right to retain your point of view, and I respect and understand you fully.  From my own direct experiences, NOT what PWK has said, I have my opinion, which I have earned a right to have, and honestly express to others.  Thanks for responding.

 

Jeff 

 

 

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No, you don't have to be careful with me. I've been doing this for awhile and I can assure you my colleagues and I are only interested in protecting the Forums and Klipsch. Aside from that, "The policy ofletting a hundred flowers bloom and a hundred schools of thought contend is designed to promote the flourishing of the arts and the progress of science".

 

However, having had the honor and privilege of spending some time with PWK, and recently the honor of archiving his 400 or so reel of tape including his stereo experiments, I can tell you this: They are equal to or superior to 98% of any recordings made since. And you are quite welcome to listen to them on my system anytime...forum members are ALWAYS welcome in my home. 

If you still think it's all about amplifiers, fine and dandy. I've always said that it's both metaphysically absurd and supremely arrogant to think I know what someone else hears. I know people who can hear differences in power cables and resistors. I don't...but who am I to doubt them? 

 

In my case, I can tell a quality recording from not-so-much on a car system. On my all Heritage system it's painfully obvious regardless of the amp running it, and I've had many from bottlehead 1w amps to megawatt amps to drive them with. Compared to the differences in source material quality, all differences are relatively minor in amps for me.

 

Dave

 

 

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2 hours ago, Mallette said:

No, you don't have to be careful with me. I've been doing this for awhile and I can assure you my colleagues and I are only interested in protecting the Forums and Klipsch. Aside from that, "The policy ofletting a hundred flowers bloom and a hundred schools of thought contend is designed to promote the flourishing of the arts and the progress of science".

 

However, having had the honor and privilege of spending some time with PWK, and recently the honor of archiving his 400 or so reel of tape including his stereo experiments, I can tell you this: They are equal to or superior to 98% of any recordings made since. And you are quite welcome to listen to them on my system anytime...forum members are ALWAYS welcome in my home. 

If you still think it's all about amplifiers, fine and dandy. I've always said that it's both metaphysically absurd and supremely arrogant to think I know what someone else hears. I know people who can hear differences in power cables and resistors. I don't...but who am I to doubt them? 

 

In my case, I can tell a quality recording from not-so-much on a car system. On my all Heritage system it's painfully obvious regardless of the amp running it, and I've had many from bottlehead 1w amps to megawatt amps to drive them with. Compared to the differences in source material quality, all differences are relatively minor in amps for me.

 

Dave

 

 

 

Golly Dave, 

 

You and I have certain things in common.  I was very closely associated with a USA speaker manufacturer by the name of Robert W. Fulton, for the last ten years of his life ( 1978-88).    He was my first audio mentor.  Coincidentally to your post above, RWF was a recording engineer, for a company he ran called Christian Dynamics in Minneapolis.

 

Your statement, 

 

" I know people who can hear differences in power cables and resistors. I don't...but who am I to doubt them? "

 

got my attention.  That is interesting to know, thanks for posting that !!

 

Jeff 

 

 

 

 

5 hours ago, Schu said:

Subbed

 

Edited by Jeffrey D. Medwin
corrected spelling

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Jeff, I've been waiting for you to surface here after a couple of guys told me what happened on AA and HH!  Welcome to the party.  Will Dennis be joining in as well?  I'm sure there are many who will enjoy reading about your philosophy of amp and speaker design.  Do you miss living in NJ?

 

 

Maynard

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