[brjernej]

Two years ago I came across G5 project. At the time it seemed to me like a rocket science, i still had complications with the hum and noise in TT pedals.
But then my friend, who is dedicated guitar player and tube fan, announced he is getting married - and I made a promise I would make him an amp head for his wedding gift. Approximately a year ago I had some time and made a plan to the extent that I did all the needed shopping. From the very beginning I had certain mods in plan, so I didn't order the "all inclusive" kit, but bought parts separately.
Almost a year passed before i was able to dedicate myself to the project again. So the friend is already married - but with all the parts there was no turning back!
So after quite some hours of work here is my rendition of G5 amp.
With following mods /variants)
- DC heater
- LineOut (as in version 1)
- Send/return is omitted but possible to add, as there is a jumpered conector on the preamp pcb
- Q regulated bias (Dymo mod) - with typ3055 transistor
- swithable "safety resistor" on the output of OT

DC heater was qite a task, since EL34 draws 1,5A when hot and even more when cold. First I planned to use a MIC295092 circuit, but then a friend gave me a cheap DC/DC stepdown module with 3A threshold, which is quite enough (and there is really no need for perfectly clear DC for the heaters, just not grossly noisy), and I hooked it after a gretz bridge and a prominent 10uF cap - I was afraid there would be problems, because the bought mains transformer had 8VAC output (I tried to plan voltages as close to the needed as possible to avoid too much of a dissipation of then planned linear regulator - so I used low dropout diodes on the bridge and planned to use low dropout regulator -well, now I know I shouldn't be so afraid of an IC warming up a little (or 100°C), and there are also heatsinks ... So, quite a lot of complication for nothing ... well, nothing, I learned: a little overvoltage is easier to regulate and cool down than to get good linear out of too small of a boundary. Well, when all hooked up, the DC supply is quiet and nice. On precisely 6,3VDC, grounded from the module to star ground. My headphones hear nothing. Ozsi shows some noise on micro scale. So, I can call it sucess. For the next time: plan power transformer heater secundary with few volts overhead so there would be no need for monster filter cap and low dropout bridge diodes

[brjernej]

To be able to plan the "guts" without drilling (and ruining with mistakes) the chassis, I made the model from the cardboard box. It proved really fantastic, much more sturdy than I thought it to be. Before that I made all plans for my projects in Corel Draw, and it was a time consuming work, but still prone to mistakes - it was much easier to work with real components - and much more fun. So all the wires, all the "modules" and parts could be positioned and dimensioned correctly (but still I made some stupid things haha).

[brjernej]

The biggest issue was preamp board etching and drilling - the later much more. I don't know, is it me, are the late hours in which I was working on the project or it is a common thing, but almost no 1mm hole was on the right place. For the etching I used a lack paper (from net from China) and pressed toner on the copper board with the help of salvaged copier fuser (I don't like to ruin my laminator; this was a separate project of mine which turned worse than I thought - on a salvaged fuser I mounted a 250°C thermostat instead of thermal fuse, but I have problems with the wheels assembly, not sure why. Still, it works quite good) . To be on the safe side with the crappy preamp board I tinned all the traces. I also put rivets in mounting holes for tube socket (so it was easily soldered on the "wrong" side) and also in all wire terminations (to be able to remove them any time without ruining the traces). Populating the board was easy work then. I have put also complete tone stack on the board - as I always leave the notches on the pots I don't beleive there is much damage done to the board through pot fiddling. But the tube socket it the other question - there is no chance you would put in or out the tube without holding the board - so for the next time: build point to point (preamp is really straightforward easy), or at least plan screw attachment holes very close to the socket.

[brjernej]

I was afraid, if the biasing board would really work (I am not used to work with sand), but it was OK. Still it would be much simpler to use a 250kLin more powerful pot. But, as it works, this design could be used on all the other future projects ...

"Switchable safety resistor" was part of the plan the whole time, the reasons are two:
1) Filip is my friend. I wouldn't like him to ruin his amp's OT by not plugging in the speaker
2) G5 is a weak amp - to get the real "sound" it should be connected through "line out" to a more powerful power amp - and then it is a nuisance to plug in its own speaker
So I bought a 50W 7,9ohm power resistor and mounted it on a switchable jack for the speaker out. I was afraid if I did all correctly, because OT's are not cheap stuff. But, it works.

I have managed to wire the line out pot in opposite (how?!?), but as it works, I will not resolder it.

[brjernej]

Final result?
The first thing, looks are amazing (let us ignore my ugly handwriting, OK?). Hammond made a fenomenal job with the chassis cover, and you don't need a lot to make the amp look like a boutique hi-fi. The "G5" letters are from automobile part of harware store, and look just right. I have put the main power led on the top of the chassis to make leads as short as possible (from the DC heater supply), but with the amber led the looks are fenomenal - amber glow of led mixes with amber glow of power tube and it's just - magical ... Power resistor on the back protrudes from the main shape, but not too much, and looks like some alien "super powered" add-on. There are some drill holes which I made out of stupidity and sloppyness, but don't bother too much.

The guts look messy as hell, after I made it I was quite ashamed of it, compared with neat insides of other amps on the net. But still, everything is on right place and there is claritiy of logic; the sonic results correspond with careful design (perfected star ground near the input jack, safety distances between modules, generous separation of signal, power and GND wiring). For later projects I work more with solid wire to ensure more neat wiring. Oh, I used speaker wire for heater supply - I am a serial overkiller, if you haven't noticed yet.
The other overkill are the capacitors: I parelelled practically all power caps with lower poly ones: for the power tube, by the OT, and used only 10uF poly for the preamp ... Probably this is far too much, but I don't know a reason this could be wrong.
You probably noticed, I am a "chocholate freak" (at least in Slovene electricians call those plastic enclosed screw terminals chocholates) - they are probably not very good in the signal path, but with high voltages in power sections they are perfect for modular building. And there are allways few there in your box. Around the OT I used them to enable easier switching between primary and secundary windings - if they prove unreliable through time, they still can be replaced with terminals. But, jacks are also just slide contacts, right? In power section use of "chocs" is logical - why solder (and then desolder, and solder ...), when screw terminals work just fine. The whole rectifier board is based on those chocs, because I planned to etch it, but then didn't feel like it. Later I will use cancaps with solder lugs attached to the chassis and also the bridge - this board is a disgrace and is bulky (and don't ask me how to remove it from the chassis). You can see the power supply is not on one place, but near the corresponding modules: a)rectifier with reservoir cap b) power tube caps (with all the psu resistors) c) preamp cap d)OT cap (parelell to reservoir cap) e) caps of DC heater. Behind is the logic, that caps must be close to parts they supply (to "embrace" the circuit).

Sound:
I hoped for a low noise build, but such ... It is a success. There is no hum, no mains, on both knobs at full there is some static, but, it's on the level of "out of shop" amps ...
At full gain overdrive is magnificent, with correct adjustments on the guitar you can get crazy things. And if you also add banana booster in the sound chain ... Sweet!
Clean sound is nice, but weak. Real tubey sound, but not at band practice volume. 25W max dissipation SE design has it's toll. Here comes handy line out jack, and with the connection of external power amp you can hear the sweetness. Tone stack is less effective than expected, with the "sweep " switch practically unnoticeable (is there some mistake?)

[brjernej]

next builds (if when and why - takes lot of money and time):
- preamp in point to point arhitecture (not Fender like, but "real" ptp, with components directly on the socket, and supported with singular terminals on other side - also the TS in PTP >> on pot lugs
- rectifier: "cube" bridge and can capactior attached to the chassis
- 9VAC secondary for the heater (to use normal diodes), maybe separate DC/DC modules for preamp and power sections
- connections made with solid hookup wire for neater (and less parasitic /capacitance) problematic guts
- bias board made on protoboard
- power psu made on terminals
- OT connections made on terminals
- use rackomount chassis with internal brackets - not so beautiful, but significantly cheaper, makes the amp more useful

[brjernej]

forgot:
- I used a custom made power transformer - toroid, which was 28€, much less than original
- regarding the sound: I suspect the treble is some way attenuated, but this could be also due to the fact I tested the amp mostly on my bass cab

[Germy]

Dear brjernej, 

as the first a question. Do you plan this forum or after this project found?

Is there an entire schematic? The construction is not especially clear and which you a fan of "chocolates"    are one sees clearly.

The central issue is, it brings fun, however, the security should always come first. Can you send a sound file? 

Greetings from north germany

Germy

[brjernej]

Oh, I see I forgot to attach the schematics ...
For the mods /differences:
a) variable bias  - g5 biasing pic
b) DC heater supply: i didn't do the schematic, but in the form of block diagram it is
PT secondary-> bridge-> reservoir cap -> DC/DC module -> both heaters
(grounded at the filter cap to the star ground, led ex
c) I documented some other change on the attached guts pic

[brjernej]

"guts"
and the "LIne out" mod

[brjernej]

Dear Germy,
thanks for the response. I am not sure if I understood your first question correctly ... My first post on this forum were approximately around the time I got the first ideas about that project - but back  then it was a fantasy for me ...

I hope I gave you enough details about the construction.

Wow, the security, yes ... There was "don't touch the wires, don't short to chassis" voice shouting all the time while testing in my head. And I had to adopt the "turn off, then test" policy - with the pedals, you just let it run and fiddle the wires. Still I suceeded to short V2's pin 3 to the heater momentarily when controling voltages, without damage dane luckily.

For the sound file you will have to wait a little, because I gave away the amp already ...

[Laurent]

Hi Brjernej,

A first build is always something special, especially with the task you wanted to accomplish (I mean a wedding gift to your friend). To build a G5 from scratch as a first attempt is quite a bit of a challenge. I think you managed it pretty well  but in some ways there are things, which cannot be neglected. For sure it would have been easier to start building your first amp with the G5 kit (with other transformers if you were on the budget) and to follow the G5 layout, which has been done by people with experience. This way you can learn things from the right way and much faster.

Anyway I'm with Germy about the fact that safety is the most important. It is even more important when the amp is for somebody else. Your friend will trust you and that would be very sad if he would get hurt by getting 300V on his fingers while playing or if his house would burn down during a short break (I know, I exagerate but this is to emphasis the importance of that point).

If I could also suggest you one other thing: I did not catch the point in having the DC heater supply for the EL34. The output pentodes are not really sensitive in getting heaters hum. Considering that those bulbs draw about 1.5A, this is a big relief when you "just" provide them with AC. In your position I'd have started to regulate to DC after the EL34 for the pre-amp only. Pretty sure you wouldn't notice the difference. This is only an advice for your later builds.
Don't forget to consider that when your EL34 draws 1.5A DC, your transformer will need to deliver 3A! That's a lot for no real result. Should you next time build a 100W head with 4 EL34, I could not imagine how big your transformer would need to be 

For your future builds, don't be shy to ask in the forum for support, starting from the design phase of your project. Here you can get support from real experts with huge experience (I take myself out of this category). This way you can make sure that your project will reach your expectations.
But again, nice first job and don't let you demotivate by our  attitude 

Cheers,
Laurent

[brjernej]

Oh, thank you for you response. It is allways nice to learn from you with all your experience.
Yes, it was quite a leap for me, from low voltage pedals to a full amp - and without my friend's wedding as a challenge I wouldn't probably do it.
Even with my first kit. TT SugarBox, I made it "my way" - I see no point in just soldering as it is in the pictures; well, I did make a big mess of a buzzing ground loop monster from this kit, but quite deeply learned about the grounding rules and techniques from this experience. And this attitude of mine goes on; with all my lack of knowledge it is funny, I know. But it is more the concept I am interested in, not drilling holes (or not even that, with predrilled chassis) and doing a nice paintjob. Again, it's true that you don't need to build an amp to test some concept if there is a friend you can ask ... Or even so much as here on this forum. I feel too "inovative" sometimes, I confess
As for the G5 kit, I see no big difference in ordering separate parts myself (and can be also much cheaper, with the right choice of providers), plus there is an extraordinary happiness to make your own BOM an order by it, not only get the box full of bags with assorted components. But really it all started with my fear that I will ruin a component (overheat it with soldering, break the lead ...) and so wanted to have few extras on hand - in the kit you only get one for every needed component. Well, I do trust myself more now (and know, that electronic components ar not so fragile as they look), but still. If it was only about getting the components from the kit together, I wouldn't do it at all (well, maybe for a friend, but not for my pleasure). It's the mods and tweaks I enjoy, and feeling smartass about them (Well, I do enjoy less all the mistakes I commit in such explorations and troubleshooting them, but I do learn something in the process - I just happened to learn that too short of a leads from the shielded cable are a short circuit playground -__-)  I thought I had enough experience from al my LoV TT projects, all sand pedals, all troubleshootings and mods of existing amps that making a "vanilla" G5 would be - boring.

As you are the second one talking about the safety I am really curious if there are certain irregularities you noticed on the pics of the amp or is it said just generally. As I am not from electric engineering field, I don't really know the regulations. I think I observed all the needed safety precautions about earth-to-chassis and ground-to-chassis connections, about arcing and cooling and about fuses. Most of it is already in the schematic. Is there a special thought / advice you would like to give me?

DC heater for all the system was a question of a stubborn concept. I've read so much about the heater hum and all the neaded precautions (but in practice, when looking at the guts of the amps most builders make a mess out of heater wiring) I said to myself, why not DC. All TT LoV projects have a DC heater - I had not only a PSU circuit, but also the PCB. Then 1,8A heater current (or even muuuch more, when tubes cold) proved more of a challenge than I expected - but still, I am in this field for challenge. So this DC heating has grown in my main consideration in G5 bulding, and all was ready to do it with a LDO linear regulator and schottkys, when a friend gave me a cheapo chinese DC/DC switcher module, which proved to be a better solution, specially with lower heat-up. Thank you about the info on pentode sensitivity to hum, it would be much easier to design (and also use 12,6V DC on preamp then). For more, eg. 4  powertubes the tranny would have to be quite big, yes, a separate toroid of approx 100VA would measure 10x3cm and have 1 kilo, in comparison with 10x2cm, 700g for 50VA (but how strong then has to be the tranny for the anodes, my god - is it really nearly 600VA?). So I was thinking to build a power switcher directly from mains voltage, or maybe just tweaking an existing 12V PSU to reach the right voltage. Or use unchanged 12V supply and then supply preamp directly and poweramp through DC/DC converter.

Now I am on the previously mentioned project Yahamaha again, to include an Alembic preamp, with the help of TT Vpump. Now I am in the phase of troubleshooting, I somehow manged to fry the Vpump module ...
Again, thanks for your attention and help.
Jernej

[brjernej]

and now the soundfile - not edited, recorded with a phone; with variable degrees of different gain, master and tone stack settings ...
https://dl.dropboxusercontent.com/u/7791647/My%20recording%20%2313.wav

[Wuffenberg]

Hi Jernej,
the lower E and A strings have a good clean punch, I like that. I hear you saying "tshisty", means clean, right?
The crunch sound seems fine. More distortion however seems still a bit unbalanced, try a bit to vay the cathode resistors and bias points.
Only that snarling backgound noise in the beginning is a bit distracting (sounds like a non-muted snare drum).

Greetings from Moscow, Tom