GM70 PP

GM70 PP monoblock

Introduction

In the past , I never intend to build tube amp that using voltage over 1000V because it is very dangerous to deal with high voltage. So I never build tube amp that using tube like 211 , 845 , 833A etc.

But a few month ago I met with my friend who have GM70PP diy amp that he not satisfaction to it and he asking me to modify it for him. After I take a look at that amp , I found that they using the poor design and poor parts also many area are still not secure to use , such as too small wiring cable , small wattage of resister and no breeder and it chassis look not so nice so I decise to re build it to new amp keeping only transformer , socket , connector and some capacitor.

The design

My new design are using Cca for input tube and split phase my Electraprint Autoformer that I success to use with my F2A PP , driver tube is 6V6 both Cca and 6V6 are using Ixys 10M45S CCS chip loading and output are Gm70 using fix bias.

Schematic

PSU

Construction

This is very big and heavy amp , I construct it to monoblock but it's still heavy , it have big Power transformer for high voltage and filarment for GM70 another trabsformer for input and driver tube , 2 big choke and the last it very big output transformer from Lundahl

All the part is using very good quality that I take ie from the previous chassis , connector are WBT for RCA and Binding post , C coupling are Mundolf silver/gold , R almost using Kiwame.

under chassis

I have some problem when I finished it , it have very lound hum , I try many method to reduce the hum , but still there untill I found that the hum is come from GM70 socket the are loosing after I fix it so everything are OK

The sound.

After I test it with my friend high end system , he using Watt/puppy 7 , Audio research reference 3 for pre amp , and CD transport are CEC with Mark levenson DAC , sorry that I forgot the model. I think it sound is very nice , strong and some backup power when playing classic , high is OK , I heard some sound that I think that I never here from SE system that he have ( he also using 300B PSE from KR enterprise ) , only middle that SE is still better but overall it's sound very good but I can't compare too other PP amp that using other tube such as EL34 , 6550 or KT88.

Currently I change the input tube from Siemens Cca to Tung sol 5687 , I think the sound are more better than Cca version , bass is more realistic also high are better too.