Thespeakerdude8
Super Member
Hi Guys! I'm building up a pair of the Baldwin 40 watt Monoblocks from the model 45 organs for Bre's Dad and he asked me to share my progress on here.
Here's how they come stock. They run a Quad of 6L6G's, one 12AX7 (earlier versions used a 6SL7 with slight changes to how the NFB is dealt with.) IIRC, the original version used 3.9k NFB resistor and inserted it below the cathode resistor for the first 6SL7 stage, the 12AX7 versions use a 39k NFB resistor and inserted it AT the cathode of the first stage. The overall circuit in them is very close to the Magnavox 93xx and 88xx amps, using a paraphase inverter and similar component values. Experts will argue that the Paraphase inverter ain't up to the task of driving a freakin' quad of 6L6's in push-pull parallel... but we'll scope it out later on. Besides, if it sounds good who cares? These amps when re-done will give a LOT of well known vintage hi-fi amps a run for their money.
He wants the chassis polished so first thing I'm doing is removing all the transformers so I have a flat surface to work with. The iron in these things is insane! The power transformer alone weighs almost 20lbs. I'm doing these one at a time so I can have a before and after reference.
Here's a test spot on one of the chassis. I'm using Mothers Aluminum & Mag Wheel compound for polishing.
Here's after one polishing with the 6" wool cutting wheel. After this they get a coat of Mcguire's carnuba wax and then clearcoat.
I took this photo on my way home from my storage unit ( had to grab some more polishing materials.) This is after the final wax and prep for clear.
More to come but I'll lay a game plan out:
-Upgrade filter caps to Nichicon UPW series low esr 105* caps, using 100uf first two stages and 47 for the rest (vs the stock 8 uf before and after the choke.)
-Upgrade coupling caps to Solen fast caps- excellent bang for the buck, going from .1uf to .22 uf to improve bass response.
-Adding binding posts for the 8 and 16 ohm outputs
-Adding high quality rca binding posts
-Adding a bucking transformer set up to buck 6.3v off the input voltage of the amp to get it down around 115v so the tubes don't red-plate. These amps WITH the bucking transformer run about 400v on the plates and run a class A idle bias from the four 6L6G's.
We'll be using old stock RCA 6L6G (coke bottle or ST shape.) These tubes sound GREAT and have a different sound than the GB's or GC's. The amplifiers were originally designed for G's, but ran them right on the edge. We'll address that later on in this thread.
After all of the cosmetic and electrical refreshing we'll hook em up to a scope and a load and play with the NFB and check frequency response, sine and square waves and adjust till it looks right- then we'll listen and adjust accordingly.
Stay tuned!
Here's how they come stock. They run a Quad of 6L6G's, one 12AX7 (earlier versions used a 6SL7 with slight changes to how the NFB is dealt with.) IIRC, the original version used 3.9k NFB resistor and inserted it below the cathode resistor for the first 6SL7 stage, the 12AX7 versions use a 39k NFB resistor and inserted it AT the cathode of the first stage. The overall circuit in them is very close to the Magnavox 93xx and 88xx amps, using a paraphase inverter and similar component values. Experts will argue that the Paraphase inverter ain't up to the task of driving a freakin' quad of 6L6's in push-pull parallel... but we'll scope it out later on. Besides, if it sounds good who cares? These amps when re-done will give a LOT of well known vintage hi-fi amps a run for their money.
He wants the chassis polished so first thing I'm doing is removing all the transformers so I have a flat surface to work with. The iron in these things is insane! The power transformer alone weighs almost 20lbs. I'm doing these one at a time so I can have a before and after reference.
Here's a test spot on one of the chassis. I'm using Mothers Aluminum & Mag Wheel compound for polishing.
Here's after one polishing with the 6" wool cutting wheel. After this they get a coat of Mcguire's carnuba wax and then clearcoat.
I took this photo on my way home from my storage unit ( had to grab some more polishing materials.) This is after the final wax and prep for clear.
More to come but I'll lay a game plan out:
-Upgrade filter caps to Nichicon UPW series low esr 105* caps, using 100uf first two stages and 47 for the rest (vs the stock 8 uf before and after the choke.)
-Upgrade coupling caps to Solen fast caps- excellent bang for the buck, going from .1uf to .22 uf to improve bass response.
-Adding binding posts for the 8 and 16 ohm outputs
-Adding high quality rca binding posts
-Adding a bucking transformer set up to buck 6.3v off the input voltage of the amp to get it down around 115v so the tubes don't red-plate. These amps WITH the bucking transformer run about 400v on the plates and run a class A idle bias from the four 6L6G's.
We'll be using old stock RCA 6L6G (coke bottle or ST shape.) These tubes sound GREAT and have a different sound than the GB's or GC's. The amplifiers were originally designed for G's, but ran them right on the edge. We'll address that later on in this thread.
After all of the cosmetic and electrical refreshing we'll hook em up to a scope and a load and play with the NFB and check frequency response, sine and square waves and adjust till it looks right- then we'll listen and adjust accordingly.
Stay tuned!
Last edited:
smilie!
Damn that looks better than I imagined!!!
