Slash AFD100 boutique amp (#34 and #36/39 in one amp)

[Antonio S]

Hello guys. All right with you? Hope everything is great.

My name is Antônio and I live in Brazil and like you, I'm passionate about vintage electronics and tube amplifiers. I'm still at a low level of knowledge about amplifiers, but I've studied and already understand some things.

The reason for my visit here is that, recently, I ordered a tube amplifier handmade by an experienced builder here in Brazil. As a good Slash fan, I immediately opted to reproduce modifications #34 and #36/39 made by Frank Levi and Tim Caswell. After a lot of research on the internet, we gathered the schematics and chose to follow the Marshall AFD100 diagram and that's how my amplifier was born.

It has a few more “features”, being a 50 watt amplifier, with 2 EL34 Tung-Sol in power and 5 12ax7WB Sovtek in pre. It has hand-wound transformers, tube effects loop and 2 fully independent channels, with individual equalizer, master volume and gain for each channel. The first channel (clean) is based on Marshall Plexi, using the original diagram. The second channel is a JCM800, with 2 keys available that activate the mods, one key for mod #34 and another key for mod #36. When both switches are off, it is a standard JCM800.

My doubts are as follows:

1. To get the #36/39 (AFD) sound, does the switch on mod #34 need to be in the on position? Because activating only switch #36/39 and leaving #34 off, it seems that something is still missing in the sound. As soon as I switch the switch from #34 to on, the sound is identical to the AFD album.
2. Are Sovtek's 12ax7WB valves influencing? I know they are valves aimed at a darker tone and maybe I'm denigrating the real sound of the mods.
3. Is it worth changing the EL34 for 6550? In the Marshall AFD100 the valves used are 6550 and in Slash's own amplifier as well.

I made some sound samples showing the different combinations of switches. It's nothing professional, just the iPhone's microphone right in the center of the speaker.

My cabinet is 2x12 equipped with 2 Celestion V30 MesaBoogie, manufactured in 1996 and the settings are: Presence: 7 - Bass: 4 - Middle:5 - Treble: 7 - Gain: 7 - Master: 2

JCM800 without mods
https://drive.google.com/file/d/1zb2_Zx ... sp=sharing

Switch #34 on and #36 off
https://drive.google.com/file/d/19DoEZX ... sp=sharing

Switch #34 off and #36 on
https://drive.google.com/file/d/1eOYeBQ ... sp=sharing

Switch #34 on and #36 on
https://drive.google.com/file/d/1Uf_FrQ ... sp=sharing

I hope you understood my doubts and I will be very happy if you can help me! I am attaching photos of the internal part of the amplifier and the schematic used for construction.

Grateful,
Antonio.