Fun with Parabees

[johnsonad]

I'm picking up a pair of Parabees tomorrow and am looking for ideas on what to do with them.  I intend to strip them of the iron and build something on a larger platform.  I'm open to ideas and would appreciate the input.  Some of you may remember that I have a pair of Paramount-ish amps currently (6sn7/300B, 350v, 50mA, -75v, 5K output).  I'm willing to build something out of the norm so please don't hesitate. 


Thanks,

Aaron

[Paul Birkeland]

I'm picking up a pair of Parabees tomorrow and am looking for ideas on what to do with them.  I intend to strip them of the iron and build something on a larger platform. 

You can buy that iron without destroying a very rare pair of amplifiers.

[Paul Joppa]

It's a good operating point IMHO (heh heh I talked Dan into it ...) If you put it on a bigger chassis, I would mount the iron for better hum isolation. I posted long ago a DC heater mod for the 300B using the PGP8.1 transformer. The TFA-2004 is magnificent.

[johnsonad]

There is some love for these amps! PB I'm torn both ways.  The price of the amps was less than the cost of new iron and was my driving factor in the purchase.  The platform was too small so they were going to get a rebuild regardless and the PS caps are getting on in years.  I'll start with PJ's idea of a bigger chassis and DC heaters for the 300B's along with updating the PS components.  Is the schematic floating around somewhere by chance and if so, may I get a copy of it?  Is there anything to update in the driver stage?

For the DC heaters with a larger chassis, I'd be willing to put in a second power transformer and a FC, Paramount style if it would be a significant gain over the other DC design.

[Paul Joppa]

With a choke-in filter, the PGP8 can power a DC supply from the 6.3-v winding - if you use low-loss Schottkies and a low resistance choke. It can power the driver too, providing heater DC voltage for hum protection at the same time. Ping me offline for details.

For modernization, I'd use the "soft-start" driver board and 5670 tube - basically turn it into a Paramount. If you are going all out, updating the power supply caps to films is always nice.

[Doc B.]

I'm with Peej, make it a Paramount. It's a better circuit. I would keep the output iron and go with a PT-4 for the power transformer.

[xcortes]

My Parabees ended up as Paramounts ages ago.

[RPMac]

Aaron, I got my Parabee's for the same reason...too much good iron to pass on. The problem I have with them is too much hum and too small a platform.

Here is the link too the PGP8.1 dc-heater mod PJ mentioned. Looks like the schematic was a victim of the site upgrade. Maybe PJ will repost it.

http://bottlehead.com/smf/index.php/topic,4266.0.html

Edit: I think this is the power supply schematic...and a thread you may be interested in.

http://db.audioasylum.com/mhtml/m.html?forum=set&n=73216&highlight=Western+Electric+M91&r=&search_url=%2Fcgi%2Fsearch.mpl%3Fforum%3Dtweaks%26searchtext%3Dphilips

I have more imagination than knowledge, but you wanted an 'out there' idea...DC heaters on the 300B and drive it with a 45.

Don't know if it is adaptable, but the heater supply on the BeePre is absolutely quite...300B or 6A3.

[Paul Birkeland]

Don't know if it is adaptable, but the heater supply on the BeePre is absolutely quite...300B or 6A3.

It is not.  The Paramount DC filament supply, however, was designed for this purpose.

[johnsonad]

Thank you guys for all of the responses.  PJ, I'll email you off line.  You all have given my something to think about.  More to follow

[johnsonad]

I got them up and running last night.  They have the original 6n1p-eb drivers and TJ mesh globe tubes.  They sound very nice but the hum has to go though it's not as bad I as expected from what Rod told me (but he is using 102dB sensitive speakers).  They had a certain ease about them that my amps didn't have which lead me to remove the grid chokes in the big amps..

Is there an easy way to know which version these are?  They have a small circuit board over the driver with two LED's if that helps at all.

Thanks!

[Paul Joppa]

The original had C4S circuit boards feeding the driver plate (pin 6 on one amp, pin 1 on the other). There should be some tiny diodes and a trimpot connected to the 300B filament terminals and/or the large hum pot. This is the Bench hum cancellation circuit; it never worked as well as we hoped which is why Paramount has DC filaments.

I don't recall any other versions of the ParaBee. Maybe someone else does? Here are the two possible variants, neither of which I consider to be Bottlehead "versions":

1) First there was a BeeGlow which was series feed with the TFA-204 (not the parafeed TFA-2004). It became ParaBee when we moved to parallel feed; I helped revise the circuit at that time.

2) The Tucker shunt regulated driver circuit, originally developed for the 2A3 Paraglow and sometimes called ParaGlow II, may have been adapted to some ParaBees.

By the way, we found after a few years that the available 6N1Ps would kind of fade after a year of hard use - if yours saw much use they may be tired now. But the amp uses only one triode and is set up so that you can swap the 6N1Ps between amps and use the other triode.

[johnsonad]

Thanks for that Paul.  I'll call Dan tomorrow and see if I can get a copy of the schematic.   

[xcortes]

If Doc's ok I have the manual as well as the Tucker upgrade manual.

[anystereo]

Xcortes,

Hi, I have long since misplaced my manual for the tucker parade mod, can you share your copy with me, even just the schematic page in pdf so i can figure out the proper install in the original parade schematic.