Paramour w/ TF-204 MagnaQuest output transformer

[mrclassicman]

There is a long story involved with this but the short version is this. I am looking for the schematic that this conversion/upgrade was. It removed the parafeed choke to the power supply and the TF 204 was then put in for the output transformer. Any information on this modification would be greatly appreciated!

[Paul Birkeland]

I suspect whether the cathode bias resistor should be changed will depend on whether you have the V1 power transformer from Hammond or the V2 power transformer from our current manufacturer (which would be labeled PT-2).  I could certainly imagine running a little more current at slightly lower operating voltage on the PT-2, but I'm not so sure I would do that on the Hammond power transformers.

[Paul Joppa]

From my notes, dated 2003:

"Airgapped Paramour
Replace the output plate choke and parafeed transformer with a TFA-204. Makes a sort of junior WE Model 91 with similar operating point. About 4.5 watts output. This is not a parafeed amp anymore, but a sweet combination in the conventional mode."

Today, I would not say that about the WE 91, but I would still note that the operating point (300v/50mA/4K ohms) is typical of many 300B amps. My own preference is for a lower power/lower distortion operating point (250v/60mA/2.5K ohms, or 275v/55mA/3K ohms, or 300v/50mA/4K ohms). The difference is small but audible, based on listening to the MonAmour at the two different currents it offers.

As PB indicated, the original Paramour used the Hammond power transformer, which is rated 55mA DC maximum. Allowing 5mA for the driver and its C4S plate load leaves only 50mA for the 2A3. I have never in the past recommended increasing the current above the rating, since I did not do the detailed design myself, and I do not know the actual winding schedule.

This was an issue with the earliest parafeed upgrades (BCP-15/BH-5) - the BH-5 was similar to a junior TFA-2004 at 3K ohms, which I somewhat reluctantly accepted when used with the 40-henry BCP-15. But the TFA-204 is only 10 henries. (We eventually commissioned a custom 4K upgrade transformer from another winder to use with the BCP-15.)

I hope that adds some context to the issue.

[mrclassicman]

Thanks you Paul & Paul. The amp is using 300B mesh plates and has a 76 as the driver. The power supply has a 310-0-310 v secondary with the appropriate 2.5 v and 6.3 v filament windings. Could the origins of this amp actually have been a ParaBee? Me and my more adventurist side made an attempt to convert these amps to use a 45. For one reason or another the outcome was way less than I had envisioned and I shelved the amps. So talking out loud here I think my best plan would be to isolate the tubes and measure my B+. Then I should have a better Idea of what to do to find the sweet spot. We built so many B-H kits and this amp is the only one without a manual. I also have to admit that it has been a very long time since I have been under the hood so to speak and need to work up some confidence ! A little like Bilbo leaving the Shire! lol Again thank you both for the tips!!!

Terry (mrclassicman) 

[Paul Birkeland]

How is a Paramour using 300B mesh plates?

What power transformer is in these amps?  Photos?

[mrclassicman]

Pardon the condition, as these where a buck to run mods on. The 300B are the 2.5v type. Sorry the attachments rotated on their own. The power transformer is a Hammond H300668.

[Paul Birkeland]

I would electrically leave everything alone and just run the TFA-204 in place of the stock plate choke.  The stock plate choke can replace the 270 ohm power supply resistor. 

You could also sell the TFA-204s and run the SEX Iron upgrade packaged (wired as 4K iron).  This would give you substantially better bass performance than both the stock iron and the TFA-204 would have, and the 4K impedance works nicely with the Paramour circuit.

[Paul Joppa]

OK, that was an original Paramour version 1.1. There seem to be other mods, notably the perf-board which I presume to be a current source but not one I recognize.

I have modified an older file to show the schematic for the TFA-204 modification. I did not include changes necessary for the 76 driver - mainly the cathode bias resistor.

Because of the limitations of the power transformer, there are not many options for other operating points.

[Doc B.]

The 300B are the 2.5v type.

That always cracks me up. Still waiting for someone to make a 1.25V 2A3. And a 5V 845.

[mrclassicman]

First of all thank you guys so much for the information. I now have what I need to decide where to go from here. I prefer not to max out the power supply as I feel head room there is a big plus. One of my 300B's was broken in shipping and I cannot justify the cost for a new one. Yes Paul you nailed it, the perf board is a Constant current source. My speakers are very efficient, room is small and my hearing is still pretty good so I am not trying to get max wattage only one or two really good watts is all I need. I am totally impressed that after this many years I am still getting valued support !  You are all AWESOME!

Terry (mrclassicman)

 

[mrclassicman]

That always cracks me up. Still waiting for someone to make a 1.25V 2A3. And a 5V 845.

Question Doc, does this actually mean the 2.5 volt 300Bn is actually a variant of a 2A3? Just a beefier 2A3? Since I am not going to replace the broken 300, I will either do a mono system with the remaining 300 or covert to 2A3's for stereo. Also I have no idea were these 300Bn's came from! lol

[Paul Birkeland]

Question Doc, does this actually mean the 2.5 volt 300Bn is actually a variant of a 2A3? Just a beefier 2A3?

It's a Chinese 2A3-40. You can take a 300B and connect one filament pin on the socket to both ends of the filament in the tube, then the other filament pin on the socket to the center of the filament inside the tube, and thus you get a 2.5V 300B.

Since I am not going to replace the broken 300, I will either do a mono system with the remaining 300 or covert to 2A3's for stereo. Also I have no idea were these 300Bn's came from! lol

The amp doesn't need to be converted to 2A3 use.  Just plug in a pair of Sovtek 2A3s and enjoy!

[mrclassicman]

Thanks Paul for the info. I was just trying to ascertain if this was just an advertising trick or a real deal thing. I have a few 2A3's in my stash. When Doc chuckled I thought I might be missing something. In a way we would do this filament thing with 12xx7's, the filaments in series were 12 volt but using the center tap of the filament we could use the 6.3 to each of the halves. Well back to the bench as the B+ seems to be a little on the high side @ (475) .  This voltage was without the tubes installed so no load voltage. I am just trying to be cautious lol. Thanks to you Doc and Paul J. for all of this assistance!

Terry   

[Paul Joppa]

Voltage will rise with no load. I did the calculation and got 474 volts, so you're fine as far as I can see.

[Doc B.]

My point is really that the iconic names get co-opted for marketing's sake. The 300B was a tube made by WE that has a filament set to run at 5V. Ergo, an amp designed to run a 300B supplies 5V to the filament pins. A tube that needs 2.5 volts to heat the filament won't plug into an amp intended for 300Bs. So it's nothing but confusing to call the thing a 300B.

The fact that most of the King Kong 300B variants that have come out over the years won't produce any more power than a stock 300B in a given 300B amp (they need a new circuit that supplies more V and I) is another case of subverting the name for marketing's sake.

I am surprised that no one in all these years came out with a tube called the 2A300B.  That would be the ultimate way to confuse the issue.