diy hiwatt 50, troublesome sound and abnormal voltage compared with schematic

[Tao1]

Hi
out of passion for pink floyd, i built a hiwatt 50 myself, this is the first time ever my life to build an amp. the first running was good, no spark. and i plugged my guitar, it works fine. But i always feel like the sound is not satisfied, it's not like the sound i heard from the demo sound from kit-rae. Because people all say big muff with hiwatt sounds fabulous.(i will attach my big muff with hiwatt sound. the demo sound from kit rae http://www.kitrae.net/music/MP3/IATsolo_EMG Strat_GRMuff_TD_FF_AS_DR103_HTCA.mp3 (which uses exactly the same version muff) i use the same amp and muff setting as him.
so i was questioning if its because of my incorrect building.
I measured all voltages.
All the voltage measurements are under the situation:
Mains and standby on, all preamp and power tubes are installed, connected into 8ohms speaker. All the voltages are measured to the ground. All the heater voltages are 6.8v( all the tubes work fine)
I found 2 problems.
The first problem: for my ecc81 phase inverter tube，the readings are
Pin1 298v
Pin2 89v
Pin3 84v
Pin6 290v
Pin8 84v
Which are massively different from the theoretical reading according to the schematic
The second problem is the v3 ecc83
Pin1 320v
Pin2(grid)87v
Pin3 84v
Pin6 226v (when I tap it with multimeter, a huge blow sound appearing from the speaker)
Pin7(grid) 0v
Pin8 1.8v
Why there’s voltage on pin2(grid) and no voltage on pin7(grid). I think grid should not have voltage for preamp tubes except for the phase inverter tube(ecc81). Is this normal?
The schematic providing actual voltages is attached
I marked all the actual voltages in green and all the theoretical voltages on schematic.
Thanks for your help in advance

 

[ruffrecords]

The ECC83 stage looks OK to me. The first grid is at 0V because it is connected directly to 0V via the master pot.

The second stage grid is dc coupled to the plate of the first stage via the 1M resistor which with th 560K forms a potential divider to bias the grid to 87V. Note that reading s of grid voltage are notoriously unreliable because of the high impedances involved. Either way the dc conditions on both halves of the ECC83 look OK to me.

The Ecc81 is a different matter. It is not exactly a conventional phase splitter. However the grid and cathode voltages of each triode are identical and the plate resistors are not that different and they are connected to the same HT supply so your measured values look about right to me. The schematic ones look wrong. So I am inclined to think the schematic itself is wrong.

Cheers

Ian

 

[Accelerator]

@Tao1​

Hi [B]Tao1,[/B] greetings from Greece, welcome aboard!...

There are plenty of infos about the legengary David Gilmour and the gear that he used and still use in the "Gilmourish" site, so take your time to take a look...

The David Gilmour Gear Guide

For the most "authentic" re-search about the Hiwatt amps schematics I highly recoment the MHuss Hiwatt Amplifier Pages - Tech Info page as they were plenty of deferent Hiwatt amps with deferent topologies back in time...

As for the deferentces in Voltage, you should have to accept that all the Guitar Amp. Power Transfomers (P.T.) have +/- 10% Tolerances and that the new Partridge (P.T.) transformers they are not so much powerful as the old one were, because the new corent production EL34 tubes could not withstand the High Voltages of +500 DC Volts HT like the old Mullard EL34 did, so all the designers of the amps and the engineers of the transformers tamed down the nearby of the +500 DC Volts that a old Hiwatt DR103 or a old Marshall JTM100 "Black Flag" amp. had...

​

 

[abbey road d enfer]

The first problem: for my ecc81 phase inverter tube，the readings are
Pin1 298v
Pin2 89v
Pin3 84v
Pin6 290v
Pin8 84v
Which are massively different from the theoretical reading according to the schematic

They are not "massively" different. They are well within a 10% tolerance, which is all that can be expected fom a tube product.
There's nothing wrong with the voltages in your amp.
The sound difference is somewhere else, tubes, transformers, loudspeaker, guitar, fingers...