Gates BC Transformer ID ??

[KB3DKS]

  I have this nice transformer that looks unused other than scratched up. It has a Gates part # of 478-0048-000 and the drawing # of AS 3158.
 It weighs 12 lbs, with two close matched primary ? windings 1-2, 3-4, about 38 ohms dcr each and two secondary 5-6, 7-8, 16 ohms dcr each. All terminals are top mounted with 3/4 inch ceramic standoffs. Audio signal tests using matching source and load impedances shows a good 20-20kc near flat response so I would assume it is possibly a driver or output of some type.
  If those of you who have Gates transmitter manuals could look at the parts list maybe an ID can be made.

It is not from a BC-1T or F

The Part # sequencing from the manuals above indicates that:
472 series are Filament/Power With a Drawing # of AF-XXXXX? & AP-XXXXX?
476 series are Chokes and Mod Reactor With a Drawing # of AC-XXXXX?
478 series are Audio With a Drawing # of AI-XXXXX? ( Input) & AM-XXXXX? (Mod)

 Following that logic AD-XXXXX? would probably be a driver, so what is AS-XXXXX?
These Drawing #s are may not be indicated in the parts list.

To help Identify old BC Iron, maybe if anyone with manuals could post the probable part #s here we can get a compilation on site for easy reference. Pix would help for those loose pieces. Not just Gates units. A lot of the transformers turn up at Hamfests but other than an obvious Mod or Plate type what is it and from where.

Thanks,
73,
Bill KB3DKS in 1 Land

[W4RFM]

Try calling 217-222-8200 for Harris parts, and see if they can identify it.  The numbers might still be in their system.

[K4AAM]

Looks like the driver transformer from a BC1F matching 845 plates to 833 grids.

[KB3DKS]

Looks like the driver transformer from a BC1F matching 845 plates to 833 grids.

  Thanks !!
That is it !! My schematic is missing the last section of the foldout which has that part of the circuit and I also found a note that the driver transformer  Drw #
AS-3158C was replaced with # 478-0048-000. So AS-XXXX? indicates a Driver
  OK, now if I had the rest of the transmitter to go with it...
I do have the PP 845 Driver deck but the LV transformer is shot. Guess the Station Engineer thought that it was a bad driver.
 The rest of the transmitter got scrapped before I came along. Only got most of the Iron from it.
  Thanks !!
Bill,
KB3DKS in 1 Land

[W4RFM]

I would still find out the "Z"s.  If the numbers are right that thing is big enough that it could be a mod transformer in your future for some serious power. 

[k4kyv]

I would still find out the "Z"s.  If the numbers are right that thing is big enough that it could be a mod transformer in your future for some serious power. 

That would be a waste.  Broadcast quality class-B driver transformers are much rarer than modulation transformers.

I haven't checked out the numbers, but it looks identical to the later BC1F 845-833A driver transformer.  It is made by Chicago Transformer Co.  The earlier models used open frame transformers made by Thordarson, in their Tru-Fidelity line.

Rated for about 30 watts of audio.  About a 5:1 step-down, primary to 1/2 secondary.  Too  much step down for a modulation transformer, and the winding wouldn't take DC because there is no gap in the core.

[K4AAM]

That Gates PP 845 driver deck with the matching transformer makes some sweet audio. I am almost done restoring one and have that same transformer  to go with my homebrew rig. A pair of 813s modulated by 833s.    Patrick

[KB3DKS]

Don,
 I have confirmed the part # is the BC-1F Driver. This one is probably a late model replacement unit as the case is not the same as the other Chicago transformers from this transmitter. The housing is capped on the top and bottom with the terminals directly mounted thru the cap not on a bakelite plate. Built like a Peerless, Saratoga or Acro. Mounting is a bottom plate welded to the cover not a flange.
 Anyway, it's a keeper as I have the matching driver deck as well.

Patrick,
 Isn't that backwards...833s modding 813s ? Sure to get more than 100%. Lots of watts of heater current ! I look forward to hearing it.

 I have to re-inventory the Iron from that transmitter to see just what I have.
Got all this about 8-9 years ago and have moved a couple times since but I think
most all the pieces for the 1F, including the Malony (sp) Mod and Reactor are there.
  Don't know what is still good. No plate Iron or matching chokes.
 
  BTW, has anybody used the Mod deck out of a BC-5P for a driver? It's a real monster using 4 EL-34/6550s to drive the UTC driver tranny that is about the size of a CVM5.

73,
Bill, KB3DKS in 1 Land

[K4AAM]

No Bill, not backward,the audio chain is out of a scraped Gates BC1F.Plenty of good clean headroom.     Patrick

[k4kyv]

That Gates PP 845 driver deck with the matching transformer makes some sweet audio.

Unfortunately, the audiophools figured  that out too, and have driven up the price of n.o.s. RCA's beyond the means of 99% of the hams.  I have seen Chinese made ones that looked identical to the old RCA's, but haven't heard how well they actually perform or how well they hold up.

But I got mine, heh, heh!  A lifetime supply of US-made 845's, used, but still check out good.  A  BC1-F driver xfmr and a spare. Audiophools, eat your heart out!

[KB3DKS]

No Bill, not backward,the audio chain is out of a scraped Gates BC1F.Plenty of good clean headroom.     Patrick

Patrick,
 Great audio chain but why 813s for RF. A single 833 or pair as in the original design would be all triode without another supply for the screens.

That Gates PP 845 driver deck with the matching transformer makes some sweet audio.

Unfortunately, the audiophools figured  that out too, and have driven up the price of n.o.s. RCA's beyond the means of 99% of the hams.  I have seen Chinese made ones that looked identical to the old RCA's, but haven't heard how well they actually perform or how well they hold up.

But I got mine, heh, heh!  A lifetime supply of US-made 845's, used, but still check out good.  A  BC1-F driver xfmr and a spare. Audiophools, eat your heart out!

Don,
 Yep, 845s are near impossible to find at any reasonable price. But the VT4-C can still be found and it is somewhat close in ratings. Could these be used rather than the 845 ?  I have a couple pair and was considering the possibility. Since I already have suitable Mod Iron this driver ties it all together. I really like the idea of a completely ballanced audio path. It preserves the assymetry of speech.

73,
Bill, KB3DKS in 1 Land

[K4AAM]

Well Bill I have a bunch of 813s on hand and as for the screen supply I use a droping resistor off the modulated H.V.   A little extra heat but simple. I just wish I had a pair of Dons American 845S in my all american rig:)   Patrick

[W2XR]

I use the Chinese-made 845s in my audio driver circuit, and have had excellent results with them. I think I paid about $140.00 for a matched pair, and several years ago I purchased (3) matched pairs which should be good for a lifetime of amateur radio usage. Comparing them to old-stock US-made 845s, I hear literally zero difference in the audio quality of my rig.

You cannot directly substitute 211s (VT-4Cs) for the 845s. The tubes bias up completely differently, and the plate-to-plate load impedance is different as well, which will be critical to the optimal usage of that Gates audio driver transformer. Since the 845s used in broadcast audio driver service are used in a self-bias topology, you will have to calculate the correct value of cathode resistor to set the bias up for class A operation of the 211s.

I run 1200 VDC on the plates of the push-pull class A 845s in my homebrew audio driver, and the total cathode current is set for 120 MA. The operating conditions for 211s/VT-4Cs will be probably somewhat similar, but you'll also get less audio output power from a pair of class A 211s. For push-pull class A audio driver service, the 845 is plainly a better tube; that's why Gates, Collins, W2XR, WA1HZK, K4AAM, and others use or used them for this purpose. Class B grids are notoriously difficult to drive, as Don/K4KYV and others have discussed on this board previously, and you need a pair of driver tubes that won't fold as the class B modulator tube grids are driven deeply positive.

And be sure to wrap the negative feedback loop around the 833As back to the first push-pull voltage amplifier stage in the audio driver; you'll clearly hear the improvement in linearity as well as frequency response.

I say the hell with it and buy the Chinese-made 845s. I purchased mine from one of the importers of these tubes; Sophia Electric in Wash., DC. , and their service was excellent.

Good luck with what will be a superb-sounding audio driver circuit!

73,

Bruce

[k4kyv]

Mike, NI4N, used a pair of 211's as audio drivers for a pair of 833A's in his BC-339.  He seemed to have good luck with them using a driver xfmr designed for 845's.  Of course he had them biased correctly.

The main issue is the plate resistance.  You want to use a class-B driver tube with as low plate resistance as possible.  The 845 has the lowest plate resistance of any of the "100-watt" class of tubes like the 211, 845 and 838.  So you could expect to get more distortion with the 211, unless you used excessive step-down at the driver transformer, but then your af drive voltage would be limited.  In the late 20's and early 30's, a pair of 845 was often run in parallel class-A for a Heising modulator.  RCA never recommended running the tube as an rf amplifier.

A pair of class-A 845's would modulate a pair of 210's or a single 211 or 203-A at less than 100 watts input.

[W2XR]

Mike, NI4N, used a pair of 211's as audio drivers for a pair of 833A's in his BC-339.  He seemed to have good luck with them using a driver xfmr designed for 845's.  Of course he had them biased correctly.

Don,

What is a BC-339? I'm not familiar with that rig.

73,

Bruce

[W2XR]

Deleted. Please see my next post on this topic.

Bruce
 

[W2XR]

 BTW, has anybody used the Mod deck out of a BC-5P for a driver? It's a real monster using 4 EL-34/6550s to drive the UTC driver tranny that is about the size of a CVM5.

73,
Bill, KB3DKS in 1 Land

Hi Bill,

I had commented on my personal experience with the EL-34 tube circuit and the later solid state audio driver unit as used in the Gates BC-5P back in March of '07.

Here is a portion of that post:

"When I worked as a broadcast engineer during my college years, I worked on the Gates BC-5P2. Not one of the best sounding rigs on the air; I think the audio driver was largely to blame for that, along with an excessive amount of negative feedback wrapped around the modulator and driver in an attempt to linearize that mess. The Gates <5KW rigs always sounded the best IMHO.

Perhaps you can straighten out that audio driver kluge that Gates designed. The later versions of that rig used a solid state audio driver that was even worse sounding and notoriously unreliable. "

Just my own observation. Others may have had better success with that 6SN7/EL-34 based driver circuit, but the general concensus in the broadcast engineering industry was that it was of poor quality.

73,

Bruce

[KB3DKS]

Hi Bill,

I had commented on my personal experience with the EL-34 tube circuit and the later solid state audio driver unit as used in the Gates BC-5P back in March of '07.

Here is a portion of that post:

"When I worked as a broadcast engineer during my college years, I worked on the Gates BC-5P2. Not one of the best sounding rigs on the air; I think the audio driver was largely to blame for that, along with an excessive amount of negative feedback wrapped around the modulator and driver in an attempt to linearize that mess. The Gates <5KW rigs always sounded the best IMHO.

Perhaps you can straighten out that audio driver kluge that Gates designed. The later versions of that rig used a solid state audio driver that was even worse sounding and notoriously unreliable. "

Just my own observation. Others may have had better success with that 6SN7/EL-34 based driver circuit, but the general concensus in the broadcast engineering industry was that it was of poor quality.

73,

Bruce

Thanks Bruce !
 Guess I will just leave that deck on the shelf till I have nothing better to do. Do not even know if it is functional as it was a spare. Would make a good basis for a high power audio amp if the driver tranny is blown ! 
 Too many parts.. not enough time!
73,
Bill, KB3DKS in 1 Land

[k4kyv]

The BC-339 uses a pair of 833A's in pushpull in the output.  It uses a balanced symmetrical pi-network tank circuit, with split stator plate tuning and split stator loading cap, designed to feed balanced feeders.  It was designed for CW and RTTY, so has no modulator.  It also uses a 3-phase power supply, which is a PITA.  Mike built an outboard modulator that also used a pair of 833A's.  The original transmitter will not go very far below 4 mHz, so some modification may be needed to make it cover 80m.  It comes in a huge cabinet, about the size of a 1 kw broadcast transmitter.  All the wiring inside the transmitter is sheathed in lead tubing.

http://www.nj7p.org/cgi-bin/millist2?mode=normal&name=BC-339  (specs)

http://jptronics.org/radios/Military/JANAP161/an.frt/an.frt-type.bc-339.pdf  (photo)

[W2XR]

The BC-339 uses a pair of 833A's in pushpull in the output.  It uses a balanced symmetrical pi-network tank circuit, with split stator plate tuning and split stator loading cap, designed to feed balanced feeders.  It was designed for CW and RTTY, so has no modulator.  It also uses a 3-phase power supply, which is a PITA.  Mike built an outboard modulator that also used a pair of 833A's.  The original transmitter will not go very far below 4 mHz, so some modification may be needed to make it cover 80m.  It comes in a huge cabinet, about the size of a 1 kw broadcast transmitter.  All the wiring inside the transmitter is sheathed in lead tubing.

Thanks for the info, Don!

Wow, that is a big xmtr, considering it was designed for CW and RTTY service only, and had no modulation capability. But then again, it was designed for military service, so there you go.

Any idea as to why the internal wiring of the rig was sheathed in lead, vs. copper or some other metallic material?

73,

Bruce

[W2XR]

Try calling 217-222-8200 for Harris parts, and see if they can identify it.  The numbers might still be in their system.

Hi Bob,

Unfortunately, most of the old Gates and early Harris dwg. numbers pertaining to the components and assemblies within their plate modulated rigs are no longer on file at Harris in Quincy, IL. This has been the case for the last 6 years or so, perhaps even longer. It's basically hit-or-miss as to what they can find. The original AC-, AD-, AM-, AP-, etc., prefixed part numbers for the Gates and early Harris magnetics were superceded by the all-numeric dwg. number system years ago. (Example: 478-0346-001, etc.).

When I pulled the magnetics out of the Gates BC-1F I obtained almost three years ago, I naturally wanted to get the original factory engineering specifications for these items. I phoned the Harris Service Department, and they were extremely helpful and accomodating, but the only specification control dwgs. for any of the magnetics within that rig Harris was able to locate was for the modulation reactor and the audio input transformer. And the dwg. Harris provided to me for the mod reactor was not even for the monster Chicago or Thordarson Tru-Fidelity 50 hy reactor originally used in that transmitter; it was for a much smaller/less inductance replacement part.

Harris stopped all support and service for the old plate modulated rigs years ago.

73,

Bruce

[k4kyv]

That replacement iron is the same as the iron used in the 1-T or later.  The newer mod reactor is about the same size as an old tube type TV power transformer, and they made a replacement for that one that is even smaller.  I use one of these in  my 8005/805 rig.  It is very bad about talking back, and I have to reduce the mic gain to avoid a squeal.

I can comfortably pick up and carry a set of the newer mod reactors and xformers in one trip without a problem, but I can hardly budge one of the original 1-F reactors or xformers off the floor.