Marshall Class 5 – Fromel Mod and New Speaker
In this video we go step by step through the Marshall Class 5 Fromel Modification as well as a new speaker and valves. Let me know your thoughts on the changes and if this video was helpful. Thanks!
Time Stamps
0:00 – Intro
0:52 – Un-modded Amp tones
4:10 – Mods and Tools
4:46 – Step 1- Mod Disclaimer
6:54 – Step 2 – Prepare the Amp
9:49 – Step 3 – Drain Filter Caps
11:43 – Step 4 – Tube PCB Prep
12:05 – Step 5 – Output Jacks PCP removal / Access Tube PCB
14:16 – Step 6 – Tube PCB Mods
18:11 – Step 7 – R25
19:28 – Step 8 – Removing main PCB
22:01 – Step 9 – Grid leak and V1 Cathode Mod
23:13 – Step 10 – Bright Cap
24:01 – Step 11 – Preamp Gain for tone stack
25:24 – Step 12 – Coupling Cap and tone stack mod
27:00 – Step 13 – Treble Peaker
27:44 – Step 14 – V2B Plate Load
28:15 – Step 15 – Cooling Bias
29:22 – Step 16 – Filter Caps
30:15 – Step 17 – Adding a Choke
32:20 – Step 18 – Putting it back together
34:45 – Step 19 – Checking you work…Sound test!
37:34 – Final Thoughts
#Marshall #Class #Fromel #Mod #Speaker
Originally posted by UCnj_yrtzsszr_Ccl2eR9aNg at https://www.youtube.com/watch?v=Kcvh3iyRZq8
Ok, there are no explanations in video what mods realy do to the sound. I was qurious to understand that, so i checked by writing my observation here. They are not scientific, they are just my understanding. R25=2,5k>10k (max alowed resistor/greed stoper for filtering hight freq on power tube +); R20=470R/1M (input impedance ?); R18=1K5>2.5k (more clipping in first stage, less gain – relevant to taste, no + or -); c8=25u>1u (less bass, voicing like first "treble" input stage in big marshalls +); 100pf on pot pins ("treblle cap" – taste. better to be swichable); Remove R7, R9, and C13 swich to 470K (simplification and going to dark side – 470k greed stoper resistor cuts more hights than 220k. Highst are added by 100p, now removed my bigger ressistor/low pass filter. Funny combination). Remove R28, C14, C20, and C21/Install 56k in R28/Install .022uf Mallory 150 in C20 and C21/Install 270pf in C14 (arguable. The best values that resolve issues for hight gain stock marchall TMB voicing are in p1 amp from ax84 project. This is in order to keep stock pots but change TMP knees); Remove R14, 470p across R12=470k. This last mod adds gain and brithens the tone. Its the most relevant to the goal of brithening amp. R13=220k>150k (reduce gain on triode). R27=150R(?)>220R. Thiss lowers tresshold to power valve clipping, reduce autput power, make sound more on the dirty side, but, prolongs tube life. Increasing values of C3, C4, and C11 is for better filtering. Choke – more noise filtering.
Such killer little amps. I miss mine all the time. Now I rock an Origin 20 which is great, but there was something really special about those little Class 5's.
algorithm for the win. very cool!