Amp Guts Photos - Official Thread - Lets see those pics

[Jeff Scott]

Hmm, this is a whole lot of text for a photo thread.

 

[agedhorse]

I looked at the circuit again, looks like 3 LTP's the symmetry and clip thresholds of each stage will be different due to base bias being different, the rounding (compliance) is simply due to the resistor feeding -15V to the collectors. These then sum. It's an interesting approach, and one that makes sense in the context of the era.

 

[Kevin Wolfe]

‘66 AB165 Bassman. Modded for guitar: extra gain stage/pot, revoiced coupling caps and running 5881’s instead of the 6L6’s. In a single 12” cab with an L-pad attenuators. Also switchable between fixed/cathode bias. The big resistor on the rectifier board is to drop the B+ voltage for running the 5881's. The tone stack is also moved downstream. The Bass channel is at original specs.

 

[disssa]

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[rufus.K]

Fend Twin Reverb II.
Rivera original.

 

[mnats]

Ampeg B-1RE

 

[disssa]

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[teemuk]

Off hand, it looks like a summing strategy. Odd way to do it imo, but we don't have insight into what the designer's intent was either.

It's a 3-band distortion, "Tricomp". Lows, mids and highs distorted individually exploiting soft clipping characteristics of differential amp. The scheme reduces IM distortion but of course changes nature of the distortion top.

 

[agedhorse]

Right, each band is summed, but I don't see much distortion unless they are either driving the diff amp very hard or are using transistors with an unusual Hfe.

I will have to do some math to see what's really going on.

 

[disssa]

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[BogeyBass]

Right, each band is summed, but I don't see much distortion unless they are either driving the diff amp very hard or are using transistors with an unusual Hfe.

I will have to do some math to see what's really going on.

Most the distortion is coming from the opamp. Aside from parallel resistors for filtering it's hard to calculate gain but in nutshell. the Min gain is around 80 to max 160 and with boost engaged about double that. Transistor acting as diodes to ground for soft limiter. Easier to get the higher voltage threshold they wanted with transistors than stacking diodes. Basically when increasing the gain it gives needed distortion saturation. but the output level won't be so jumpy with the limiter. since with distortion devices with gain of 200 plus get rather jumpy. Filtering is working sorta like frequency dependant slew limiter. Helps smooth out the distortion in nutshell.
Problem everyone has faced with high gain distortion. I've done similar soft limit circuit to try to keep output level the same no matter what the gain setting. Just used LEDs in opamp feedback cause they had high 3 volt forward voltage and increased that to about 5 volts with simple inline resistor. Using 3 filters like they have done HP, LP, BP but with opamps

 

[tubedude]

Latest all tube point to point design here. This one for guitar. Still etching bronze barstock for control panel.

 

[NMO]

Ashdown ABM-600 EVO III
View attachment 3234250
View attachment 3234261
Upgrades:
- Silent fans: Noctua NF-A8 (with the same airflow but less than half the noise)
- Mumetal shielding around the transformer (-6dB of hum, measured through DI)
- Tung-Sol 12AX7 (V1 selected)

It looks like they still use the evo 3 pre and power amp, they only upgraded the EQ print on the front of the amp.

 

[svtb15]

I had the 500 years ago. Great sounding amp... I've been wanting to try one of these 600s..

Ashdown ABM-600 EVO IV


Upgrades:
- Silent fans (with the same airflow but less than half the noise)
- Mumetal shielding around the transformer (-6dB of hum, measured through DI)
- Tung-Sol 12AX7

It looks like they still use the evo 3 pre and power amp, they only upgraded the EQ print on the front of the amp.

 

[Rickett Customs]

Did this one several years back, Mojotone 50 watt bass amp. Definitely loud for a little buggar.

 

[NMO]

I had the 500 years ago. Great sounding amp... I've been wanting to try one of these 600s..

Yeah, it's a very versatile amp to create whatever sound you like thanks to the 9 band eq.

 

[Bassist30]

Here are some shots of a new design I'm building the cab for. The gut shot was taken before the ground buss was installed, so the unterminated leads go there. I built this as a practice amp for my annual family reunions. I built 4 single 12" tube combo guitar amps, so this completes the set, freeing up seats for the rest of the fam in the living room as the players sit on their amps.
The keyboard player stands in the corner, now I just need a solution for my drummer brother.
Oddly enough, I jacked this amp into a Blue Dog, and with the Strat it sounds better (if less versatile) than my guitar amps!View attachment 3121350 View attachment 3121352

Tell us how it sounds when completed.

 

[Rockbobmel]

Reeves C225 and TAD KT88

 

[tubedude]

Tell us how it sounds when completed.

Sounds amazing! Loud for a mere 20 watts. The trem design (stolen from Aiken) sounds great playing Starship Trooper.

Tell us how it sounds when completed.

Here's a finished image.

 

[Mr. Foxen]