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MQ introduces a new limited series of output tranneys

205.188.116.9

Posted on May 14, 2004 at 08:31:51
MQracing


 
Hi folks:

Here is a newly designed series of output transformers that I've wanted to build for a long, long time. The aim of the series is twofold. First is to offer a transformer for folks who are bi-amping and don't need the huge inductances and core capabilities of say our FS-030 output transformer. The second aim/goal was to make it good enough (full range) to serve as a high quality entry level output trans.

But... I did not want to do the so-called "universal" type output trans... where by mischeivious juggling of voltage ratios you make beleive that your trans is at one time a 2.5K, 5K or 10K trans.... physics just doesn't work that way or co-operate with that strategy in most cases...

yet... I wanted some flexibility in the design... so here is what Robin Hood and I came up with....


The "Robin Hood" name in honor of the man who took from the rich to give to the poor.... will be available in the following configurations...


All are 5K primary impedances with a UL tap at 50%. The first three models are designed to carry unbal dc currents. The last type (appropiately labeled) is for parafeed applications.


******************************************************************
RH-80

5,000 ohm pri with 50% UL tap

8 and 16 ohm secondaries

80 madc unbal current capacity

20 henries of primary L

15 watts @ 50 hz power capability

small signal response (varies a bit with source impedance) should be good from about 25 hertz to 25,000 hertz minimum.

recommended applications: high current 300B


********************************************************************


RH-60

5,000 ohm pri with 50% UL tap

8 and 16 ohm secondaries

60 madc unbal current capacity

30 henries of primary L

10 watts @ 45 hz power capability

small signal response (varies a bit with source impedance) should be good from about 25 hertz to 25,000 hertz minimum.


first example from WE for 300B

plate volts 350

grid bias -76

dc plate current 50 madc

5000 ohm load impedance

6.2 watts output

second and third HD; -30db and -45db respectively

Here is a second example from WE for 300B

plate volts 400

grid bias -87

dc plate current 60 madc

5000 ohm load impedance

8.3 watts output

second and third HD; -30db and -46db respectively


********************************************************************

RH-40

5,000 ohm pri with 50% UL tap

8 and 16 ohm secondaries

40 madc unbal current capacity

40 henries of primary L

5 watts @ 30 hz power capability

small signal response (varies a bit with source impedance) should be good from about 15 hertz to 25,000 hertz minimum.

recommende applications: this configuration is designed to support the 45, 71A and other similar triodes.


********************************************************************

RH-PF

this is the paralell feed Robin Hood.

5,000 ohm pri with 50% UL tap

8 and 16 ohm secondaries

ZERO madc unbal current capacity

greater than 200 henries of primary L with M6

12.5 watts @ 20 hz power capability

small signal response (varies a bit with source impedance) should be good from about 10 hertz to 25,000 hertz minimum.

recommended applications: many, many known applications

Please note: the parallel feed version can be custom built on nickel lams or the new generation "domain refined" silicon steel laminations. Inquiries preferred by phone for this option.

********************************************************************

These are really nice coils... and we didn't skimp much in the goodies department. All of the RH series are made with teflon insulation on the inside. All soldered connections are made with silver bearing solder. All units are housed in a brass channel frame with easy to solder to lugs.


I will *probably* only offer this series for a very, very short period of time... Robin Hood doesn't give a poop... but I ain't gonna get rich building these :=) Plus... it's more fun to do limited series of tranneys...

so... if your interested... you can sign up for your choice of the RH models outlined above for $75 each.


Please, please, please... these are the ground rules....

1) delivery will be four to six weeks out.... please don't send me an email in four days asking if your order has shipped... it will not have been shipped this early....

2) these are only available through MQ directly... you must call or email to get on the list. we accept payment via paypal or USPS money orders only. Paypal address for me is acrosound@aol.com

my phone number is 215-288-4816.

feel free to ask any questions on the forum here re: the RH series....

and if you guys can help fill in some apps for the differing models that would be much appreciated....


enjoy,

Mike

 

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Some addtional electrical and mehanical specs for Robin Hood series, posted on May 14, 2004 at 08:49:07
mqracing
Manufacturer

Posts: 4322
Joined: June 29, 2000
Hi folks:

left out some electrical data and wanted to give mechanical (size) info on these guys....

on the electrical front... the DCR of the primary for each model (doens't change) is nominally 180 ohms.


the mechanicals are as follows.....

housed in channel frame

monting dimensions 3.5625" center to center of mounting ears

overall height 2.5"

overall width 2.25"

overall length 4.0625" end of mounting ear to end of mounting ear

thanks,

Mike

 

So you can have your CAKE and eat it..., posted on May 14, 2004 at 09:02:10
Bas Horneman
Audiophile

Posts: 3951
Joined: March 28, 2001
Great thing you're doing Mike!

Cheers,
Little John..

 

Re: SE/UL 6V6 or 6BQ5?, posted on May 14, 2004 at 17:19:49
AstroSonic
Audiophile

Posts: 963
Location: SE Pennsylvania
Joined: January 25, 2003
Mike,

Would the RH-60 be suitable for SE/UL with a 6V6 or 6BQ5? I was thinking of using the Mullard 6BQ5 SE design, but with UL connection.

Best,

Bob

 

that's exactly what I had in mind :=), posted on May 14, 2004 at 18:15:37
mqracing
Manufacturer

Posts: 4322
Joined: June 29, 2000
I really wanted to have a UL capable se output trans...

one correction... the ul tap is at 43% not the fifty percent I mistakenly typed in my original post.

MSL

 

How do you use the UL tap on parellel feed?, posted on May 15, 2004 at 07:56:51
This sounds really interesting to me.
Thankx
Michael

 

Mmmm ... 6BQ5 U/L, posted on May 15, 2004 at 10:19:53
Paul Joppa
Industry Professional

Posts: 6993
Location: Seattle, WA
Joined: April 23, 2001
Fond memories, though probably 40 years old. The first amp I built of my own design used a 5kCT military surplus transformer in SE ultralinear with a 6BQ5. Got a back-loaded horn with 8" EV fullrange for free when a friend of my Dad converted to that newfangled "stereo" stuff. As I recall, it sounded really sweet.

Without feedback, the output impedance will be a little higher than SET, though much lower than pentode/tetrode. Maybe a damping factor close to 1 rather than 2-3 like SETs (or 1000 for solid state!). With the right speakers, magic!

 

Re: MQ introduces a new limited series of output tranneys, posted on May 15, 2004 at 10:48:45
Kyle K
Audiophile

Posts: 174
Location: Mililani
Joined: November 6, 2000
You said you didn't intend for these to be "universal" OPT's, but could one get reasonable performance using an 8 ohm load on the 16 ohm tap? Say, for a 2A3 application where you will not need the full power capability of the transformer?

 

let's work it out and see...., posted on May 15, 2004 at 11:45:11
mqracing
Manufacturer

Posts: 4322
Joined: June 29, 2000

Hello Kyle:

you wrote;


:::You said you didn't intend for these to be "universal" OPT's, but could one get reasonable performance using an 8 ohm load on the 16 ohm tap? Say, for a 2A3 application where you will not need the full power capability of the transformer?::::


let's see where this goes... here is how I would evaluate it....

your impedance ratio from the 16 ohm tap to the full primary is 312.5:1 which means that if you use this tap then the reflected impedance to the primary is 312.5 times the value of impedance hooked to that tap.

your idea/proposal is to use an eight ohm speaker on the sixteen ohm tap... if we do this.. then the reflected primary impedance will be 2500 ohms.... which is what a 2A3 frequently likes to see as a primary impedance.


Let us assume your using the RH-60... most 2A3's are run at 60 mils of plate current. so far so good.


firtst thing I notice is that our dcr is going to be a bit high.... the dcr of the RH-60 is 180 ohms. Relative to a 5K primary 180 ohms is quite respectable... about a .4 db insertion loss or thereabouts... but for a 2.5K primary the copper resistance is on the high side.... so our insertion losses will be greater... probably not the end of the world...

inductance wise.... we are still energizing the same number of turns on the same size core with the same size air gap... so we will have 30 henries of primary L available.

Now... ratio'ing down.... this actaully sort of helps us... 30 henries at 30 hertz will have an inductive reactance of 5655 ohms... which is more than 2 times the 2500 ohm impedance reflected to the primary... so we will gain bottom end extension (i.e., we will get better bass)....


if we calculate the phase angle of our load impedance... ratio'ing down to 2500 ohms will actually give us a moreso non-reactive effective impedance.... see our website for a discussion of phase angles as they relate to primary impedances.... but... make a long story short... we aren't getting hurt here...

Now let's see what our power delivery capacities and capabilities are. Suppose our output power from the single 2A3 is 3.5 watts. Across 2500 ohms. therefore, our AC signal volts at full power will be 93.54 vrms.

Now... our airgap hasn't changed... it's fixed... but our ac flux would change. If we kept the same low frequency cut-off point as published for the RH-60 (45hz) then we would operate at considerably lower flux density then the design center of the RH-60 since it was rated for 10 watts output at 45 hertz.

skipping through a few computer iterations in preparing an answer for you... allow me to get to the punch line....

with a 2500 ohm primary and 3.5 watt output and 60 mils of dc current... you would be able to deliver full power down to 20 hertz before hitting our pre-established maximum flux density limit... so, again, your in pretty good shape....

so...now we know the core is robust enough electrically to handle your intended full power down to 20 hertz in this modified application....

but... do we have sufficient inductance to go that low.... the -3db power low frequency limit is that point or juncture wherein the inductive reactance equals the reflected impedance. 30 henries at 14 hertz has an inductive reactance of 2639 ohms which is just a little higher than 2500 ohms. the inductive reactance of 30 henries at 143 hertz is about 2450 ohms... so we would say that our -3db point will be at 14 hertz....

so... in this case we will run out of magnetic headroom before we run out of "inductance"... in-other-words the allowable flux density limits us to delivering 3.5 watts at 20 hertz.

Not so bad... heh?


As a further study.... let's see if we get into trouble with temperature rise either in the copper circuit or in the core....

the RH-60 if operated at it's published design center... has a coil temp rise of approx 16 degrees C and a 3 degree C rise in the iron....

your proposed modified operation of the RH-60... will result in a coil temperature rise of 13 degrees C and an iron temperature rise of 1 degree C.

so.... your not going to run into any problems here either.... but this is some of the stuff your should check in making these kinds of decisions...

Conclusion... unless I've missed something.... I stand corrected in my dire, dire warnings... the only penalty we've been able to identify in your proposed use/application is that your insertion losses are going to be a bit higher... and I'm too lazy to calculate this out.... but as an estimate I would say that your going to have around a .65 ot .7 (point six five to point seven) db insertion loss... if you can live with this.... it's a bit higher than I like to design at... you should be fine....

I hope I've been helpful....

but... recall... this is ratio'ing down NOT UP... if you wanted to ratio up... it would not have worked out nearly so well...

moral of the story is... ratio'ing down generally only penalizes you in respect of increasing your copper losses.... ratio'ing up has many more penalties due to the finite inductances of the transformer and the greater magnitude of signal volts required for a given power level... so that the core will get taxed moreso... but.... that's a different study... just trust me on this :=)


MSL



 

Thanks, Mike! (nt), posted on May 15, 2004 at 11:56:06
Kyle K
Audiophile

Posts: 174
Location: Mililani
Joined: November 6, 2000
.

 

Re: How do you use the UL tap on parellel feed?, posted on May 15, 2004 at 18:56:44
MQracing


 
Hello Braubeat:

the UL taps are on the coil mostly for the airgapped versions wherein the power supply is in series with the primary winding of the trans...
then you just hook it up a you would any UL circuit configuration.

The parafeed implementation uses the same coil.... as the RH-40, 60 and 80... and, hence, it too has the ul tap by default.

running UL with parallel feed while not technically impossible... is so cumbersome that I can't imagine anyone doing it....

you would need to have a DC screen supply and a plate supply each of which was in parallel with respect to the signal and you would need to use a blocking cap (as far as I can tell) btwn the screen and the UL tap as well as btwn the plate and the plate lead on the output transformer.

Like... I hinted at.... the ul tap was incorporated into this design to give folks more flexibility in the range of applications that this trans would be suitable for. Though, i clearly envisioned that the UL taps would be most likely used in the RH-60 model in particular.

hope I've answered your query,

Mike

 

OOOHHH!, posted on May 15, 2004 at 23:09:45
badman


 
The 'lil one looks good for me, I'll probably be in touch. Question! What material did you use for the lams?

 

UL tap on parellel feed?, posted on May 16, 2004 at 07:45:25
Sector-7G
Audiophile

Posts: 11765
Joined: May 14, 2002
HEY-Hey!!!,
The parafeed UL is an interesting proposition. SE and UL but with DC-Free primary L.

There are a few options, and depend on the plate load. An inductive plate load will need a larger B+ for the screen signal than a CCS type. The goal will be to provide a low output z screen supply, modulated at the UL tap's fraction of plate signal.

A cathode follower, or source follower will do an adequate job. Set up a seperate rail, at 2x B+, and self bias a cathode follower at what ever fraction of B+ you want the screens to operate at under idle. cap couple its grid ( or gate )to the U-L tap, and you're off to the races.

For a low voltage tube like an EL84, an IRF820 might be a reasonable choice, or a 12BY7 ( relax Eli, there won't be enough folks doing this to make them any scarcer for your Brown Monster ), or maybe a 5687...
regards,
Douglas

 

Try it and find out?, posted on May 16, 2004 at 09:56:12
Paul Joppa
Industry Professional

Posts: 6993
Location: Seattle, WA
Joined: April 23, 2001
There are several posible approaches, as suggested by Mike and Douglas below. I have never heard of any results - probably someone in Japan has done it though!

A related problem is to simulate a tap where one does not already exist. I have heard of an unsuccessful attempt to use a cathode follower driven by a voltage divider between plate and ground, and direct coupled to the screen grid. Apparently it would rather be an oscillator than an amplifier. So as with any new or untried circuit idea, experimentalists should budget some time and effort for debugging.

I hope someone tries and posts the results - but it probably won't be me!

 

Treble problem though?...., posted on May 16, 2004 at 10:13:40
Paul Joppa
Industry Professional

Posts: 6993
Location: Seattle, WA
Joined: April 23, 2001
Depends on how much interleaving of course. The transformer will have both leakage inductance and capacitance. Together these will resonate at some (usually ultrasonic) frequency. By cutting the load impedance in half, you will reduce the "Q" of that resonance. If it's already overdamped, then you would lose treble; if it's underdamped you might just get less ringing. In my subjective experience, underdamped sounds better as long as you don't lose more than a few dB at 20kHz.

Here's a thought - with an active crossover, run a 45 for the treble at 5k, and a 2A3 or 300B at 2.5k for the bass.

 

RH core mats...., posted on May 16, 2004 at 10:21:02
MQracing


 
Badman. Hello. And thanks for posting.

Standard core material for the RH series is anticipated to be M6. This would hold across the RH-40, 60, and 80 models. In the RH-PF model we will offer a wider range of optional core mats including M4, M3, and nickel at this time upon application of customer.

cheers,

Mike

 

perhaps... and you make a good point...., posted on May 16, 2004 at 12:42:09
mqracing
Manufacturer

Posts: 4322
Joined: June 29, 2000
Hi Paul:

Within minutes of hitting the send button... I was already thinking of writing an addendum pointing toward the consideration you mention above re: leakage inductances, cacpacitances,and etc.

I had thought of pointing out that ratio'ing down... though much more preferable (i.e., not as harmful as ratio'ing up in most cases)... still... none-the-less is not a substitute for the proper part for the job....

so... that... say a 2.5K "Friar Tuck" trans... built along the same performance profile as the 5K Robin Hood... would look quite different electrically and be moreso optimized for 2.5K as opposed to a ratio'ed down RH. I agree.

the 2.5K trans would have fewer turns, thinner pads btwn windings, and the net leakage inductance would be half of the RH at 5K. And since the AC voltage gradients are different... the insulation package would be different and optimized for the 2.5K impedance.

So... yep.... "universals" aren't optimized fully for each condition and that is an argument I've made for years and basically why I still prefer to recommend that folks use transformers at their design centers.... i.e., use them where they have been optimized.

now...imagine a 5K three way universal.... rig it for 2.5K, 5K and 10K... and then study it's performance... do FR tests at each impedance, calculate insertion losses, do square waves to see how each tap will behave differently, do low frequency power response plots for each.... and you would find that the unit behaves best at it's nominal design center.

"Universals" (one size fits the skinny, medium and fat man) are great for manufacturer's because they can offer or cover three or more different applications from one transformer... but... does each of these "impedances" have equal performance for each tap or operating point? Nope.

In the case of ratio'ing down (as the poster orig inquiried about)... far less harm is generally imposed on the performance.... not ideal by any means... because your moving away (by defintion) the ideal (optimized) point of operation.... by less harm than ratio'ing up...

and after studying the original posters idea... I was a bit surprised, that the RH actually moved perhaps less off of "ideal" than I might have suspected... hence, my willingness, to provisionally back off of my *dire* warnings.

if the Robin Hood series goes well perhaps we should follow it up with a Friar Tuck series for 2.5K or 3K. For there still remains no equal substitute for using a properly designed part at it's design center for the job you need to do...

MSL

 

Re: perhaps... and you make a good point...., posted on May 18, 2004 at 12:47:43
Kyle K
Audiophile

Posts: 174
Location: Mililani
Joined: November 6, 2000
Still, though, for seventy-five bucks each ya gotta admit it's an attractive and versatile option compared to a lot of other alternatives out there.

 

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