Jeffrey Jackson's amp

"Jeffrey brought an eighty pound one and a half watt amp.  It used mesh plate 2a3's and was parallel feed with MQ cobalt output transformers and serious vintage power supply iron and oil caps." 

The Mill's horn system- 2 Altec 515 woofers in a highly modified, sealed RCA horn enclosure, commonly called the Ubangie. RCA 18 cell multicell horn with two RCA 1428B field coil compression drivers crossed at 300hz, Bill Woods AH conical horn with another RCA 1428B crossed in around 1000hz, Fostex Lab Series supertweeter crossed at about 7Khz. These are the speakers that all the amps played on, unless they were located in a different listening room.

Doug Eisemann showing Jack Roberts how he massages the amps to "warm them up."

Closeup of Randy Carter's entry in the heavyweight division- 845 SET. See more pics and writeup below.

Ex RCA Cinema Products engineer Hans Dietze trying to measure the inductance of a plastic bag.

Amp at left- . Amp at right is Douglas Piccard's, aka Sector 7G: The amplifier is PP HY69 finals. Front end is a cascode diff.
amp rigged for E-Linear NFB via 30% taps in the anode winding. The output transformers are modified Peerless S-265-Q. An additional tap at 30% was added, and is used along with the original 50% tap configuration to provide balanced plate-to-grid NFB for the finals. The final's g2 are rigged to 50% Ultra-Linear with the stock tap location in the outputs. With 310V B+, the amp is full Class A, and delivers 6 Watts. I discovered afterwards that switching to 30% U-L yeilds a 50% increase in power."

The Mill's horn system- 2 Altec 515 woofers in a highly modified, sealed RCA horn enclosure, commonly called the Ubangie. RCA 18 cell multicell horn with two RCA 1428B field coil compression drivers crossed at 300hz, Bill Woods AH conical horn with another RCA 1428B crossed in around 1000hz, Fostex Lab Series supertweeter crossed at about 7Khz. These are the speakers that all the amps played on, unless they were located in a different listening room.

Doug Eisemann showing Jack Roberts how he massages the amps to "warm them up."

Closeup of Randy Carter's entry in the heavyweight division- 845 SET. See more pics and writeup below.

Ex RCA Cinema Products engineer Hans Dietze trying to measure the inductance of a plastic bag.

Amp at left- . Amp at right is Douglas Piccard's, aka Sector 7G: The amplifier is PP HY69 finals. Front end is a cascode diff.
amp rigged for E-Linear NFB via 30% taps in the anode winding. The output transformers are modified Peerless S-265-Q. An additional tap at 30% was added, and is used along with the original 50% tap configuration to provide balanced plate-to-grid NFB for the finals. The final's g2 are rigged to 50% Ultra-Linear with the stock tap location in the outputs. With 310V B+, the amp is full Class A, and delivers 6 Watts. I discovered afterwards that switching to 30% U-L yeilds a 50% increase in power."

Bill Wood's new cast aluminum conical horn driven by a JBL 175 on an Onken bass enclosure with JBL D130 15 inch woofer. See other pics for Bill's crossover tool, which he demonstrated with this mono rig. Great sound out of a "mini" size system.

RCA MI 12182 monobloc amplifiers modified by Hans Dietze to use Tung Sol 6550 output tubes for 60 watts per channel. These amplifiers were demonstrated with the RCA LC9 speakers. Even the low powered triode brethren showed respectful signs and some muttered amongst themselves.....

Breadboard Bill Woods used to demonstrate crossover design. This is an excellent tool to quickly change components to create the right crossover for any given application.

Jonathan and Tom Ruppert perching on an RCA LC9, one of the best vintage two way horn systems ever built. It features a one inch compression driver on a wide dispersion radial horn, and a specially designed 15 inch woofer, horn and reflex loaded. The design's strength is the coherence of wavefronts and integration of high and low frequencies.

Jack Roberts' 7F7-6BL7GTA Amplifier-

"Uses one 7F7 driver tube driving 2 6BL7 output tubes. Does not have tube sockets, all wiring is soldered to tube pins (!!!!!) Teflon coupling caps. Battery bias. Ultra path on output tubes. Outboard power supply, 3 chokes in series on driver tube. Ear tweaked with resistors and caps. Compact design, makes for limited size of amp- this results in short wiring paths and isolation from induced resonations."

Each amplifier patiently waited its turn, with little jostling or squabbling.

Jeffrey Jackson and Jim Dowdy Lama debating solder types. Publicly.

A preamp by Josh Stippich of Electron Luv fame. Brought by Steve Blair, but so top secret nothing can be said about it.

RCA MI 1425 field coil 8inch cone driver, in sealed horn enclosure, brought by Vintage Tom. These overlooked field coil drivers sound great in their passband.

Shot of the Mill's RCA 845 monoblocs in a converted RCA rack with the new AL4-300B driver amp. This amp, with a massive offboard power supply, can either be used to drive the RCA power amps or used on its own for typical 300B SET power levels, via Western Electric facimile output iron. Circuit design by Paul Den Hollander of Leiden, Netherlands.

Steve Schell of Cogent True to Life Loudspeakers and Doug Eisemann wondering where all the amps went? AUDIO

Rear view of the AL4/300B driver stage amplifier. Built on wood as a prototype. The finished version will be constructed on a sheet of heavy copper.

Randy Carter's Manly Man 845 Set Monoblocs-



"il Monstro is a really heavy low-voltage 845 amplifier inspired by the Sakuma 845:845 amplifier from the Japanese Direct Heating site. 845 has an earned reputation for excellent sound and this design uses the same tube for both driver and output positions for a very pure tone and huge dynamics. Il Monstro was an exercise in excess, using an heavy overbuilt power supply with huge reserves from readily available iron while investing in Magnaquest and Peerless signal transformers. Chassis has vibration control layers and signal sections are separated from power supply with both shielding and distance. Actual signal path, excluding iron windings, is less than ten inches.

Features include:

        845 driver and 845 output tubes
Choke loading for both 845 tubes, aka 'Parafeed'

        Monoblock design with each channel having a dedicated power supply (100 lbs) and signal chassis (42 pounds)
         Choke-filtered filament supplies for 845 tubes
        600 volt B+ supply with 83 mercury vapor rectifier, low-resistance chokes, and oil 'motor-run' capacitors
        Peerless vintage microphone transformers for input stepup, switchable phase control
        Magnequest interstage autoformer and pinstripe output transformer under cover plate
        Rebuilt all power supply transformers with vibration control and non-magnetic hardware
        Figured maple chassis frames with heavy copper chassis plates and paduak socket trim plates
        Isolated polycarbonate sub-chassis for signal tubes

Web page on il Monstro:

For schematics:

Dorothy Woods shows the correct way to polish a husband's horn.

Vintage Tom posing for some soft core speaker "porn" with a RCA 1425 field coil driver.

Rick Henthorn's "Lefty-Loctal based DHT (1LE3, good memory Douglas! :-), TVCs, Plate Load Chokes, Parafeed output trannies, and outboard power supplies (not shown in the pics).  One day I'll get around to a proper chassis."

OswaldsMill newest addition- prototype AL4/300B driver amp built in the same style as the RCA MI9355 845pp amps its designed to drive.

Power supply for Randy's 845 amps.

Doug Piccard (Sector 7G) Linestage-

"The linestage is built around the 12B4A with active plate
loads. Gain is ~6. The power supply is choke input with 816
Hg-vapour rectifiers and an Amperite delay relay for the plate
transformer. B+ is shunt regulated to 300V for both channels
with a pair of VR150 gas regulator tubes on each side. Filament supply is separate, and is choke input filtered and regulated DC."

The real reason its called "The Tasting."

Steve Killian's "a Not-quite-done-Parabee-wannabee with a dozen or so mods.  Thanks Jim and Randy.  I think I will cryo the screws next. To a Dixie Bottlehead, it's a muscle amp." 

Herbert Jeschke, aka Mr. Voight Pipe and co sponsor of the Tasting, reviewing plans to make the Tasting a franchise.

Assembled crowd enjoying the Mill's new 182 inch plasma TV.

Rich Drysdale, aka Cogent True To Life Loudspeakers, hanging out with the locals .

Bill Woods provided yet another in depth, extremely informative computer aided presentation on crossover design. Here are some notes from his talk-

"The difficulties involved in passive crossovers can be very frustrating, to say the least.

Crossovers for horns are the most difficult due to the distance between the drivers.

It is best to cross over well within the passband of the horns. Usually one would try to x-over according to the directivity of each horn.

Conical horns have the most even pattern due to their straight sided walls. In addition to choosing a slope sharp enough to protect the driver, it is necessary to maintain good phase as well. Phase is the ability of the system to overlap evenly without one stage conflicting with the other. This can be done by adding the appropriate notch filters in the circuit.

The choice of values is determined by the target crossover points, the driver impedance, and the out of passband behavior of each driver/horn combination. You must have accurate instrumentation to do this

Bill did a crossover “on the spot” and then played the system as proof of concept.

Most agreed the sound was very good with a JBL D130+ Onken box design, ant the AH! 700 horn + JBL 2410 combination.


One final step is to LISTEN to the system over a period of time to be sure the sound is smoothly integrated. There is always a “best fit” situation in crossover design, there is no perfect crossover.


You can read more about crossovers, and see test curves at Bill Woods acoustichorn.com website.

Dixie Bottleheads hanging tight.

Nathan Lewis's room, as described by Gary Bronner-

"....we listened to Nathan's field coil Fertins driven off of his massive batteries. He had a tweeter on top which turned out to be a bit too bright, thus it was turned around to just give a bit of room ambience. The red dac was Nate's non-oversampling dac. And the amps we were using were some Class D digital amps that I brought - Flying Moles. Those are the small black boxes with green labelling.
It all sounded surprisingly good, although subsequently I've found some digital amps that I like quite a bit more than the Flying Moles.

Nate's description-

"Nathan Lewis brought a pair of Fertin 8" field coil fullrange drivers in 50 liter bass-reflex boxes, which were run to good effect in the Mill's smaller room with Gary Bronner's Flying Mole digital amplifiers. The Fertins' coils were powered by a 25Ah SLA battery. Nathan's homebrew zero-oversampling DAC based on the Phillips TDA1541 converter, feeding an output stage based on a CCS-loaded Raytheon 5842 (WE 417A clone), served front-end duties."