New build 2nd gen hybrid reverb with high plates on v1

[norburybrook]

Erwin,

High pates on V1. Is that 220-150k- 4.7ufx 2 3k3-2k2? 150k slope?

M

[erwin_ve]

Erwin,

High pates on V1. Is that 220-150k- 4.7ufx 2 3k3-2k2? 150k slope?

M

yes, but 100k slope.

[norburybrook]

Erwin,

High pates on V1. Is that 220-150k- 4.7ufx 2 3k3-2k2? 150k slope?

M

yes, but 100k slope.

and did you wire the Jazz/rock...Mid/deep like the 2nd gen or like the hybrid layout?

[erwin_ve]

Erwin,

High pates on V1. Is that 220-150k- 4.7ufx 2 3k3-2k2? 150k slope?

M

yes, but 100k slope.

and did you wire the Jazz/rock...Mid/deep like the 2nd gen or like the hybrid layout?

Like the hybrid layout. It has a few errors, but tackled it.

[groovtubin]

AWESOME ERWIN!!!!!!!!!!!!!!!

[erwin_ve]

Thanks Jim!

Further testing,

The bias voltage for the reverb driver /recover was too high. Altered the dropping resistors in the reverb filter to 470R-1k-1k. Voltages are in spec now.

Bias for the output tubes raised to 37mA.

Then I did balancing the PI:
A dummy load 4 R to speaker output.
Tone generator 100hZ/ signal direct in the PI till there is 12.5v at output scoped(not using the loop as entrance but the actual cap for the PI)

IMG_20190516_111556.jpg

Measured signal with scope is +/- 12.5V (8.5v RMS) P=V*V/R= 18W

IMG_20190516_111218.jpg

Balanced the pi with Multimeter at the 1R cathode resistors, turning the trimpot till 0.0 is there

IMG_20190516_111516.jpg

When making the signal smaller this happens.

IMG_20190516_111242.jpg

IMG_20190516_111410.jpg

[erwin_ve]

When making the signal bigger this happens.

IMG_20190516_111335.jpg

IMG_20190516_110224.jpg

As you can see; around 12,5v ppV the balance is ok @ PI. making the signal bigger leads to inbalance; when making the signal even more bigger the inbalance is bigger. Same applies for a smaller signals than the 12.5V ppV.
At balanced output there are less overtones(lets say at pick attack) and more overtones when the signal gradually fades out due to the inbalance.

The procedure is based upon this post in topic: https://ampgarage.com/forum/viewtopic. ... 48#p216778 so thanks Ayan.

Also thanks to Tony in this topic: https://ampgarage.com/forum/viewtopic.p ... er#p376547

[norburybrook]

scopes....Audio generators.....test tones.......


all above my pay grade......




M

[erwin_ve]

scopes....Audio generators.....test tones.......


all above my pay grade......




M

It's not that difficult; as simple as reading a multimeter. Super handy for troubleshooting, balancing and power output measuring.

[rccolgan]

really great stuff and making it your own! I'm digging the PCB approach too.

[erwin_ve]

Removed the frontplate vinyl sticker and replaced by a brushed alu anodized frontplate.
Much better

[norburybrook]

Erwin,

That looks amazing, great work man. Have you built a combo shell yet? what colour tolex/suede/grill are you going with?


It's a great sounding amp, and it has spring REVERB I should hack away at one of my current amps and do the same.


M

[erwin_ve]

Yeah I like the looks of brushed alu, was expensive but worth it imo.
I have a busy time coming up and the combo shell may take a while. Not sure yet what to do, maybe blue tolex with vox diamond black grillcloth.

[norburybrook]

Yeah I like the looks of brushed alu, was expensive but worth it imo.
I have a busy time coming up and the combo shell may take a while. Not sure yet what to do, maybe blue tolex with vox black grillcloth.

you can never go wrong with black Vox grill cloth on a Dumble type amp IMHO.



M

[erwin_ve]

Made 2 little recordings.

One is made with drive channel and fet engaged and a bit of the amp reverb, in jazz setting mid full up. Strat with bridge single coil.

The other is clean only in jazz setting mid full up. Reverb a tad higher. Strat with neck single coil.

Both are recorded just above conversation level.