Marantz Model 8b Stereo Vintage Tube Amplifier Fully Restored
Monday, December 26th, 2022
Marantz Model 8b Stereo Vintage Tube Amplifier Fully Restored. For your consideration, we have the venerable Marantz Model 8b Stereo Tube Amplifier. This unit came to us in working condition, and was pretty much all stock, aside from a screen grid resistor that had been replaced. The selenium rectifier was also still in place. While we know that some collectors prefer to leave these units completely original, you must keep in mind that this amp was manufactured in the 1960′s, so we prefer, in part for safety reasons, to go through and selectively restore them using modern components. All parts that were carefully removed, have been saved and will be included in the sale. They could be reinstalled if one would choose to do so. While the outside of the unit has some scratches and blemishes, it still presents itself very well. Inside the unit is very clean. The unit comes with a set of 4 Electro Harmonix EL34′s, 2 GE 6GC7′s, and 2 Motorola 6BH6′s. All tubes tested well on our Amplitrex AT1000 tube tester. After we restored the unit, I took it home for about two months and ran it in a modest system in my living room. I really enjoyed having it and replaced it with another 8b that we also recently restored. I don’t know if I will be able to let the second one go as I really fell in love with the 8b. These vintage amps were manufactured when street voltage was lower than todays. While not required, we prefer to run them through a variac set to 117 volts. This unit is highly collectable, but it also needs to be used and enjoyed. It is set up for another 60 years of faithful service. While we service most of the units that we sell, we were fortunate to have the extremely talented Ben Hase of Novalux Stereophonic do the work on this highly collectable unit. Ben is very experienced, talented, and extremely intelligent. Anyone who is able to get a piece of gear that he has restored is very fortunate, as his work is impeccable. The following restoration work was performed on this amp: Power supply rebuilt: – Original caps disconnected, but left in place – Voltage doubler caps mounted in existing side clip – Multi-section cap relocated to vertical terminal strip, original color code maintained – Diodes replaced with modern UF4007 – Added thermistor for inrush current limiting Bias Supply Rebuilt: – Replaced selenium rectifier with silicon diode – UF4007 – Double axial capacitor replaced with (2) single axial caps – Cleaned bias selector switch Signal Path Component Check: – Loaded in tubes for a base line test, post power supply rebuild – Both channels working normally – 2 of 4 screen grid resistors drifted. All 4 screen resistors replaced with 10% Carbon Comp (new production Kamaya) – 6.8 Ohm resistor on one tube socket drifted out of tolerance – replaced with period correct Allen Bradley carbon comp – Paper capacitors replaced. 022uF w/Polypropylene film caps – 15uF axial electrolytic caps replaced Final Testing and Alignment: – Retested after aging parts replaced – Set Bias and tested both channels to 40watts at 1% THD – Calibrated AC Balance at 35W output – Distortion less than. 05% at 10W – 1KHz into 8 ohm load – Set up for long term stress and listening tests – PASS The amp will be carefully packed in a heavy duty box, and surrounded on all sides with several inches of polystyrene foam. Water activated, fiber reinforced tape will be used on all box seams. We will then double box the amp, suspending the inner box within the outer for further protection. This unit is highly collectable, but it also needs to be uséd and enjoyed. The following restoration work was performed on this amp. Original caps disconnected, but left in place. Voltage doubler caps mounted in existing side clip. Multi-section cap relocated to vertical terminal strip, original color code maintained. Diodes replaced with modern UF4007. Added thermistor for inrush current limiting. Replaced selenium rectifier with silicon diode – UF4007. Double axial capacitor replaced with (2) single axial caps. Cleaned bias selector switch. Signal Path Component Check. Loaded in tubes for a base line test, post power supply rebuild. Both channels working normally. 2 of 4 screen grid resistors drifted. All 4 screen resistors replaced with 10% Carbon Comp (new production Kamaya). 6.8 Ohm resistor on one tube socket drifted out of tolerance – replaced with period correct Allen Bradley carbon comp. Paper capacitors replaced. 022uF w/Polypropylene film caps. 15uF axial electrolytic caps replaced. Final Testing and Alignment. Retested after aging parts replaced. Set Bias and tested both channels to 40watts at 1% THD. Calibrated AC Balance at 35W output. Distortion less than. 05% at 10W – 1KHz into 8 ohm load. Set up for long term stress and listening tests – PASS. The amp will be carefully packed in a heavy duty box, and surrounded on all sides with several inches of polystyrene foam. Water activated, fiber reinforced tape will be uséd on all box seams. This item is in the category “Consumer Electronics\Vintage Electronics\Vintage Audio & Video\Vintage Amplifiers & Tube Amps”. The seller is “recordmarthifi” and is located in this country: US. This item can be shipped to United States.
- Brand: Marantz
