Marantz Model 5 Monoblock Amps Restored/Serviced

Marantz Model 5 Monoblock Amps Restored/Serviced. For your consideration, we have a pair of the rare and amazing Marantz Model 5 Monoblock Tube Amplifiers. These units came to us from the son of the original owner. Included with the amps are the original owners manuals, and an original advertisement page with all the specs and pricing. We chose not to power them on, and instead had them serviced as we had no idea of the service history.

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, including the selenium rectifiers, 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.

All tubes tested well on our Amplitrex AT1000 tube tester. The tubes included in the amps are: 2 x 6BH6 GE 1 X 6CG7 RCA and 1 X 6CG7 (MIGHT BE RCA, BUT NOT SURE) 4 X EL34 SVETLANA 2 X GZ34/5AR4 AMPEREX HOLLAND BUGLE BOY After we restored the unit, I took it home for about six months and ran them in a modest system in my living room. I really enjoyed having them.

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 these highly collectable amps. 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 service and restoration work was performed on these amps: Make: MarantzModel: Model 5 (Monoblock Pair)S/N: 2342 / 2667Restoration Date: July 2024 Restoration S/N: 2342? Leakage test fail on 2 section negative bias cap - got hot during leakage testing?

032uF 22uA of Leakage - Replaced? 26uF 312uA Leakage - FAIL - Replaced? 026uF 2uA Leakage - PASS - Replaced?

Rebuilt Multi-section cap under chassis? Checked meter with bias probe - bias needle indicates 50mA plate current. Set Bias and AC Balance with test set of Mullard XF2 EL34 Restoration S/N: 2667? PS Oil Cap - 6.72uF 730uA Leakage at 500V? Multi-section Cap - FAIL 2 - 51uF - Not Tested for Leakage3 - OPEN4 - 30uF with High ESR?

2uF 236uA Leakage - FAIL - Replaced? 0355uF 36uA Leakage - Value Fail - Replaced?

Rebuilt multi-section cap under chassis? Found extra resistor added between pin 8 and pin 1 on B output tube. This took thecathode resistance for the output tubes to ground from 15K to 7K. Solder looked like ithad been manipulated, no other pictures of 5's showed this change and neither does theschematic. Removed extra resistor, now both amps measure 17 ohms from Pin 8 toground.

Checked meter with bias probe - bias needle indicates 51mA plate current. Set Bias and AC Balance with test set of Mullard XF2 EL34 Bench Tests:? 2342 shows a bit of high frequency ring on 1KHz square wave test. The effect is minimal and only worthmentioning because there is a slight difference channel to channel?

Slight channel imbalance which was corrected by swapping the 6BH6 tubes from amp toamp. Both amps test to around 35W before hard clipping? Tested distortion (THD+N) at 1 and 30W (Rated Power) Left = 2667, Right = 2342 -Panasonic VP-7725? 5% 20Hz - 10KHz, 1% at 20KHz - PASS Listening Tests:? (2) 10 hour stints of continuous running?

Listening Test - PASS The amps will be carefully packed in heavy duty boxes, and surrounded on all sides with several inches of polyethylene foam. Water activated, fiber reinforced tape will be used on all box seams. The tubes included in the amps are. 1 X 6CG7 RCA and 1 X 6CG7 (MIGHT BE RCA, BUT NOT SURE).

2 X GZ34/5AR4 AMPEREX HOLLAND BUGLE BOY. After we restored the unit, I took it home for about six months and ran them in a modest system in my living room. This unit is highly collectable, but it also needs to be uséd and enjoyed.

The following service and restoration work was performed on these amps. Make: Marantz Model: Model 5 (Monoblock Pair) S/N: 2342 / 2667 Restoration Date: July 2024. Leakage test fail on 2 section negative bias cap - got hot during leakage testing?

1uF filament supply bypass cap - trace leakage? Tested PS Mylar caps - Perfect for Value & Leakage? PS Oil Cap - 6.82uF - 530uA Leakage at 500V - OK to Stay? All sections of multi-section can test OK for value and leakage.

2 - 47uF - Leakage Pass 3 - 51uF - Leakage Pass 4 - 27uF - Leakage Pass. Set Bias and AC Balance with test set of Mullard XF2 EL34. PS Oil Cap - 6.72uF 730uA Leakage at 500V?

2 - 51uF - Not Tested for Leakage 3 - OPEN 4 - 30uF with High ESR. This took the cathode resistance for the output tubes to ground from 15K to 7K.

Solder looked like it had been manipulated, no other pictures of 5's showed this change and neither does the schematic. Removed extra resistor, now both amps measure 17 ohms from Pin 8 to ground.

2342 shows a bit of high frequency ring on 1KHz square wave test. The effect is minimal and only worth mentioning because there is a slight difference channel to channel?

Slight channel imbalance which was corrected by swapping the 6BH6 tubes from amp to amp. Both amps test to around 35W before hard clipping? Tested distortion (THD+N) at 1 and 30W (Rated Power) Left = 2667, Right = 2342 - Panasonic VP-7725?

5% 20Hz - 10KHz, 1% at 20KHz - PASS. (2) 10 hour stints of continuous running? The amps will be carefully packed in heavy duty boxes, and surrounded on all sides with several inches of polyethylene foam. Water activated, fiber reinforced tape will be uséd on all box seams.

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