John Warren

I had one and managed to score a second. They express voltage on a log scale allowing 5 decades to be captured on the swing of the needle pointer. Useful to measure voltage across a load resistor for amplifiers under test. The right unit is the first issue, 1968, all gold traces. The left unit is the last year of manufacture, 1976, Pb-Sn traces. That unit also needs a knob, which I found on-line and ordered! Measures both VAC and VDC from 1mV to 100V and dB equivalents.

Losing djk was a big hit to the local audio community in general. I miss his contributions here and elsewhere.

It's a statement amplifier: Carver has decided the vast majority of buyers are too stupid to know better.

Boards came in a bit earlier than expected. Checking first that the pc board hardware can be installed. Bass and treble pots. I'll start a separate thread on the preamp. Board mounted RCA terminals as inputs.

It's bone stock with added traces to probe the behavior. There will likely be a few components that differ from the OEM configuration to accommodate for any instabilities that might occur. Those are flushed out on at test. The board contains two independent channels with bass and treble pots. A log taper level adjust will be on the chassis. No additional mode selectors will be considered but the board allow for then to be added. Also, I used the same component IDs on the board as is on the OEM schematic so you can follow along at home!

Yes. I've wanted to get this going for some time. The boards are due in on the 19th from the supplier. Takes a morning to assemble then test!

100_UL_Screen_Grid_Dissipation.pdf

Let's break out a 12AX7 preamp board from the LK72 schematic. I managed to squeeze both channels including bass and treble potentiometers on a 2-layer, 6.6x3.18" board (the max size allowable before incurring a much higher fabrication cost). Requires two inputs: 255VDC (anode) and -45VDC for filament heaters. Simulated bandwidth using LTSPICE. Input will be adjusted using external audio taper potentiometer.

What's an A55G?

How to rate your service tech? A wee test: Capable of working amps others have butchered, including those with highly regarded reputations. Has spectrum, distortion analyzers and other expensive, well maintained analytical instruments everywhere. Manages 20 pounds of unusable, trash shipping materials for each amp received Enjoys spending endless hours figuring how to pack each amp and get it shipped so the carriers can damage it. Maintains vast inventory of difficult, hard to find electronic parts Has a source for free, low production rate transistors sourced from factory authorize distributors Buys nothing from NTE Sees one-of-a-kind factory designed parts that break when touched a "challenge" Has a source for free shipping materials such as cartons, packing foam, tape Highly skilled, former McIntosh certified repair tech Somehow possesses a viable business model with shop labor rate $8/h

Here's the schematic I used. XLi1500 120V Schematic.pdf

Did the factory offer cabinets with edge exposed plywood? Top sections look DIY. Does the badge shown in the photo jive with 1988?

Plot at left show current flow in bottom half of output tube primary (blue trace, I(L13)) and black trace top half I(L8). Summation is red trace (I(L13) + I(L8). Same current plots as above but with addition of grid and anode voltages for each pentod3 (U2 is plotted top, U3 bottom) Blue plot is current trace on secondary running thru 8 Ohm resistor (1.2A RMS), black is current in primary (89mA RMS). Secondary current is ~13.5x wrt to primary.

The plot below is a simulation of the Scott clone 299C bandwidth and phase to 100kHz. The schematic is shown above but a few of the values shown there have been revised to better approximate the amplifier configuration tested. The Hammond 1650PA, 6600 Ohm input impedance output transformer is modeled based on the specifications provided by Hammond (input impedance, DCR each winding, primary inductance and leakage). Below is measured response of the amplifier. Reasonable prediction of the result.

The plots I posted were for another circuit, not the Scott. My apologies!

I purchased the scope when I was 29 years old from the on-site Tektronix FS engineer while I was working at Raytheon Microwave Power Tube Laboratory (Waltham, MA). That was in 1987!. Also, it's a 465 but from the photo could be a 475.

wrong amp

425VDC center tap out sim v. measured.

DC rails

Plots show rectifier tube turn on current thru D1 side of 5AR4 (black) and voltage at Pin 4 (red). Blue is power dissipated by R48 which, at steady state at about 5 seconds, is ~12WRMS.

I didn't bother modeling the AC entry module EMI/RFI filter I installed on the unit I built. Transformer coupling coefficients are set at 1.00 but are generally lower. Transformer resistances are measured immediately after shutdown while still hot. Capacitors are modeled with series and parallel parasitic elements (Rser, Lser, Rpar, Cpar, RLshunt) Filaments are modelled as pure resistances Wall power is perfect, 60Hz sinusoidal although noise and HF artifacts can be added. Rectifier tube 5AR4 has parameters in the tube sim that simulate rail sag (not easy but did it!). Speaker load is 8 ohm non-inductive resistor but reactive loads can be simulated easily.

Here's a model the Scott LK72 (minus the phono pre), thought some here would be interested. The tube models are both my own and a few found on the web. I'll first post a few screenshots of the schematic and the run a few sims to show what's possible. Some advantages of running a simulation before committing to hardware: Determine dissipation power of components, find hot spots and size accordingly View current waveforms Peak-to-peak voltages Bandwidth, instability analysis and compensation Output transformer loading Predicted behavior with reactive speaker loads Overall model: Power supply transformer: Power supply: Channel A: Channel B:

I spent time with this combination Faital and B&C drivers for Klipschorn. The net was a bit complicated but overall, the sound was quite good and blew away the stock hardware, not even close. The frame was designed to slip into the top of the Klipschorn

use it as a center channel amp

Maron's wife, through an friend of hers, contacted me after his death. She had a long Excel list of hardware he owned. It's not clear to me how she came across my contact info. He either instructed her to contact me or found my contact information in his personal papers. Either way, she asked me to evaluate the list and estimate sale prices so she could sell it without getting short changed. She didn't want to deal with buyers directly and I didn't want to take the task on of being a middle man. I thought about buying the whole lot but I'm past the point of collecting vintage hardware. There were many JBL vintage pieces.