My first Design (Hey Folks! ^^ )

[Asdain]

Hello Amp Garage Community,

I Had a Hammond 370HX, and a 125ESE lying around and decided to build a little something with a single ended 6L6 GC.

so i looked up a fender 5f2a and started to tweak the design a Little and this is how it looks now:

[IMG:159:113]http://i1123.photobucket.com/albums/l552/asdain/Amp%20builds/th_loewenherz-1-rev08.png[/img]


The Tonestack has a lot of damping, but i wanted to try it. If it sucks i can put in the original Fender.

I want to build a half open 12" Combo with this, not yet sure what speaker i want ^^

Any Comments, Critics, Inspirations, Ideas or Spam on the Design ? ; )

[Super_Reverb]

I have a similar SE design that uses a 6550. One suggestion is to make provision to insert a series resistor (50-100 Ohms) between the silicon diodes and first filter cap - can use to tailor the envelope.

Also, are two preamp stages going to give you enough voltage gain to sufficiently drive your output tube? One suggestion is to add a second 12AX7 to your design. Could use three common cathode stages and maybe one cathode follower. Cathode followers can give you improved tone if used properly.

I'd experiment with bias levels in your preamp stages. Some guys alternate hot and cold biasing in three or four stages. Also, IMO, it's worth your time to experiment with smaller - 75K or so plate resistors to sweeten your tone up.

One thing you get with the FMV tonestack is fairly prounounced midrange attenuation. It's not the only design, but a lot of people use it in its various forms.

Could also add a high cut option (cap + pot) from 6L6 grid to ground or on 6L6 plate to ground

my 0.02


rob

[Asdain]

Thanks for the 2 cents

i will experiment with both higher and lower plate-loads.
the one 12ax7 should be enough to drive the 6l6 hard, although im not sure if thats still true when i use the moonlight tonestack, because it hase a lot of damping i think at least -9dB..

i wanted to stick with a one-Knob Tone stack. so if the Moonlight doesn't work i'll switch to the original Fender Tweed control.


Then this will basically be a hot rodded Fender Champ/Princeton.
(with a way oversized PT)

[rdjones]

Just a couple minor observations ...

I see what appears to be a lot of NFB, when the feedback knob is at full.
Maybe increase R17 a bit, or put a series resistor with R13 to ground for the FB point.

The 1 Ohm test point should reference to ground not the top of R16.
Again, minor, but makes taking this measurement easier when your meter's negative lead is already connected to ground.

I don't care for series connected output jacks, especially in the presnce of a impedance switch. Short only the main speaker jack.

The 2 HT fuses are effectively in series, only one is needed if used between CT and ground.

At first glance, the primary of the PT looked wired wrong for 230V, but I see now it's 2 transformers.

I'll bet it works fine as-is, though.

rd

[Asdain]

Just a couple minor observations ...

I see what appears to be a lot of NFB, when the feedback knob is at full.
Maybe increase R17 a bit, or put a series resistor with R13 to ground for the FB point.

the value of R17 and the whole NFB structure is taken from the Princeton 5f2a Schematic, i merely added the 250k pot, however i think it has a lower impedance speaker. if the NF is too strong i will attach it to the 4 Ohm OT lead.

The 1 Ohm test point should reference to ground not the top of R16.
Again, minor, but makes taking this measurement easier when your meter's negative lead is already connected to ground.

i see your point, i never really cared for that so far, but i'll try to do it like that in the layout.

The 2 HT fuses are effectively in series, only one is needed if used between CT and ground.

Its true that they are effectively in series, but one fuse between ct and ground is not sufficient for maximum safety (refer to merlins book, etc)

At first glance, the primary of the PT looked wired wrong for 230V, but I see now it's 2 transformers.

it IS One Transformer for both High Voltage and heaters. It has 240V and 220V Primary. my Wall Voltage is 230V

I'll bet it works fine as-is, though.

i hope so

[Asdain]

ok i switched back to the 5f2 tonestack with a mod i found on the internet (but with 500k potis for now) and incorporated the VVR instead of a MV

[IMG:159:113]http://i1123.photobucket.com/albums/l552/asdain/Amp%20builds/th_loewenherz-1-rev08.png[/img]

[David Root]

I would put a gridstopper on V1B. Depending on how much treble content you get, lots I think with that 10K on V1A, I might change V1A gridstopper to 22k or 33K, then V1B gridstopper should be good around 47K or 56K.

If you find you need more gain, try 120K/1K8 or 150K/2K2 in V1B, assuming you want the basic Fender low-plate 100K/1K5 tone to predominate from V1A.

I like that VVR circuit, a lot simpler than some I've seen! What is Q1?

[Asdain]

Ok i updated the rev 0.8, i think its build ready now ^^

i will put in an an old battered 'test' chassis first and test a few different components / values.

the cabinet will be a slightly modified and non tolexed 5e3 cab.
im not sure about the speaker yet,.. any suggestions ?



[IMG:159:113]http://i1123.photobucket.com/albums/l552/asdain/Amp%20builds/th_loewenherz-1-rev08.png[/img]

[rdjones]

[IMG:159:113]http://i1123.photobucket.com/albums/l552/asdain/Amp%20builds/th_loewenherz-1-rev08.png[/img]

I'm still seeing 2 references to "R2" (3 counting the VVR)

Also, I think the fat switch would be more effective with a lot higher value at "Rb", at least 100k or higher.
Otherwise, the .68u value may be being swamped.

As far as speaker goes, it would be good at first to have something "honest" and balanced/accurate so as to be revealing of the amp as it progresses and not add a lot of it's own color. EV ?
As the amp is finalized, then get woolly with something Jensen-ish.

rd

[Asdain]

Sooooo,... i spent the major part of today doing a layout in sPlan 7,
its the first version and might be full of errors, but it shows the idea ^^
What do you guys think ? does anyone see any major flaws ?

[IMG:159:113]http://i1123.photobucket.com/albums/l552/asdain/Amp%20builds/th_loewenherz-1-rev08.png[/img]

EDIT: ok it is full of major flaws, but i fixed those on paper for now and built a test version ^^

[Asdain]

so i fixed all the errors in the layout and built in in my old test chassis... result: kinda cool, but not very versatile sound... i think i might wanna go for a FMV-style tonestack and a second preamp tube. i hear some people have tried a SE version of the trainwreck express, so i did some searching and reading and now am working on a somewhat similar design known as the "derailment". when i have the schematic done i will post it again