Standel 25L15 Inspired Amp

[HotBluePlates]

So, each of those drawings (debugging aside, as in the bias circuit) may produce good-sounding amps. I don't know, because they're unusual enough you'd have to build or breadboard it to know for sure.

[teisco88]

Hot Blue Plates,

I would be very interested in working from an accurate schematic to build myself a replica 25L15 amp strictly for myself--with no commercial applications or intentions to reproduce the circuit for others.

Any help would be much appreciated, especially given the inaccuracies present in the schematics that are commonly available on the net.

Thanks!

Teisco88

[tubenit]

I would be very interested in working from an accurate schematic to build myself a replica 25L15 amp strictly for myself--with no commercial applications or intentions to reproduce the circuit for others.

HotBluePlates addressed the issue regarding sharing the schematic earlier in the thread. Someone was gracious enough to share information with HBP but with the understanding that he would NOT pass that information on to others. I know HBP well enough to know that he is an honorable man and keeps his commitments on something like that.

If anyone truly wants to build one of these, I'll pass your contact info on to the person who provided me the info from an original, documented 25L15. He's tight-lipped on the stuff because apparently the modern Standel company hassles people who make clones or something similar, even though there's no patent on the circuit. I think he wants to avoid a silly lawsuit and protect the owner of the amp who made it available to him to document.

Having said that, ............. IF you read carefully HBP's response to the schematics that were posted, you could probably make a reasonable "guess" on how to approach an amp design that would head the tone direction of the Standel.  Remember, even HBP varied some from the schematic in his tube choice.

With respect, Tubenit

[smackoj]

That is a very cool piece of tube amp americana. nice work all around fellas. Can't wait to hear the engine roar though.

FWIW regarding the actual Standel scheme, it appears that some diligent investigating has turned up a couple viable 'look-alike' schemes that could be used to make a close cousin to the Standel. HBP is clear that his representation is not spot-on accurate either.

In reality, how could any of our builds now be dead accurate? Practically none of the parts available in the 40's and 50's are available now....maybe something built the same way, but not "with the same materials".... how could that be possible? There is no human way to build a 'dead-on' accurate reproduction of any of the true vintage classics so if someone else out there wants to follow HBP's lead on a Standel build, go for it....don't worry if you don't have the same drawings Hot Blue had....something close is probably the best you can do anyway....And besides, tuck it into a hot evening gown cabinet like Tubenit designs, and nobody is gonna know if there's a modified 'Champ' under the hood!

Just one man's opinion FWIW

 

[tubenit]

In reality, how could any of our builds now be dead accurate? Practically none of the parts available in the 40's and 50's are available now

I like your perspective! Think about it ........... ZZ Top doesn't try to do La Grange like they do on their recordings. It's a great approximation instead of a perfect clone.

Some of the Dumblish clone guys seek out to buy vintage parts to build exact clones. That's seems to be alot of effort to something that may be of very little benefit because of how vintage parts values may have drifted, IMO.

With respect, Tubenit

[HotBluePlates]

I would be very interested in working from an accurate schematic to build myself a replica 25L15 amp strictly for myself--with no commercial applications or intentions to reproduce the circuit for others.

HotBluePlates addressed the issue regarding sharing the schematic earlier in the thread. Someone was gracious enough to share information with HBP but with the understanding that he would NOT pass that information on to others. I know HBP well enough to know that he is an honorable man and keeps his commitments on something like that.

Thanks Tubenit. I passed along the contact info of the person who provided me the details of the 25L15 in a PM so that Teisco might approach the source directly.

[HotBluePlates]

There are initial sound clips in this thread about my upgrading my new Gretsch 5120.

Once that guitar is done (I really hope my backordered parts show up soon), I'll stop using the same guitar and tone control setting, and show ya what the amp can really do.

[eleventeen]

Magnificent woodwork!

[HotBluePlates]

... HBP is clear that his representation is not spot-on accurate either.

In reality, how could any of our builds now be dead accurate? Practically none of the parts available in the 40's and 50's are available now...

I think I meant to address this earlier.

My amp has 3 added controls, and deletes a channel rarely used by folks that play these. The added controls can each be set to exactly match the stock circuit (2 of the do this by dialing to one extreme of the control's range).

That said, the man who provided me the info for this build was given access to an original early-50's 25L15 with a pretty strong pedigree. I'm absolutely confident in being able to reproduce the original sound.

Some songs by a guy with one of the other clones, who has more chops than me and spends the time to record the songs properly:
Bring Me Sunshine
Higher Ground
I'll See You in My Dreams
Dream Train
(All songs played by Richard Hudson)

I chose not to go the full-clone route, but others who built one of these from the same info have done that. The gold amp in the pic below is the original 25L15 and the other 3 around it are clones that were made by the guy who gave me the info. The folks he made those for are die-hard Chet fans, and just had to have the amp accurate in every detail. I was less worried about cosmetics and more about sound.

And this thread from the Chetboard shows one of these exact clones. You'll have to take my word (unless you scour the web for some photos in the back of the amp) that even where there appears to be a lack of "fit-n-finish" it's just like the original was.

[kingplank]

I want to build the Standel 25L15 but I am confused to which schematic to use.
The late Teb Weber had written in one of the forums that he Pennebaker JP 25 was the real thing; I am not doubting Ted at all; he was an amp repairman for many years and had worked on all kinds of amps.
Than there may be several iterations of the 25L15; if so, I am most interested in the one Cliff Gallop used with the original. Blue Caps.

Anybody that can guide me to the right direction or any help will be apperciated

[HotBluePlates]

I want to build the Standel 25L15 but I am confused to which schematic to use.

I can tell you for certain neither of the Weber schematics are accurate to the original 25L15. Zero doubt about that. However, they may sound similar (I don't know cause I haven't built them). You will absolutely need a JBL D130 to get the original sound, though I know some have preferences about whether to use the paper-dome version instead of the original aluminum-domed version.

Follow the Chetboard link I posted earlier. Send a PM to "ParkelCEO" or to Bill Park. ParkelCEO has been inside an early '54 25L15 which was made right before the batch sold to Hamk Thompson.

... I am most interested in the one Cliff Gallop used with the original. Blue Caps. ...

So the trivia seems to be Grady got one of Hank Thompson's Standels, and that's what Cliff used in the studio. The downside is that Bob Crooks did voice each amp to suit the buyer, so it's possible there are differences between the one I had information for and the one Cliff used. However, MBL on this thread says his sounds 100% like Grady Martin, so... MBL got the same info from the same place I did. You can see he went for more of the exact clone.

The only thing is you'll have to do everything from scratch. If you talk with the gentlemen I pointed you to they can give you every detail, but no one makes anything ready-made for these amps. So this could be considered a difficult build only because you need the ability to go from a blank canvas to finished product.

[clyde]

Quite the journey, kudos to you.  I like the spirit of the quest into the great unknown.  I'm reminded of a fellow that built an early 20th century racing motorcycle from some surviving pictures and not much else. 

[plexi50]

So this could be considered a difficult build only because you need the ability to go from a blank canvas to finished product.

Thats the rewarding thing about bare box chassis and starting with the tube punching and preamp layout
When your finished you look back and wonder how you did it all

[kingplank]

Thnaks for the replys especially HBP.
So I understand that there are possibly no 2 Standel 25L15's that are identical; I am going with my take as an experimental 25L15 with many tone options, bias select, etc. Then it will be possible to be very versetile to to emulate say, Grady Martin or Chet. Even Grady sounds different on every session so even if I am getting close it is possibly good enough.
Here is my modified Bob Crooks schematic, with additional adjustments on the first preamp section, and a full Baxandall tone control on the second. I am going to use 6L6's for now, as there are no 807 available in Western Canada
Please feel free to comment and suggestions, before I start drilling holes.

[tubenit]

Thanks for sharing the schematic.  My only comment is that on V1 using a 270k plate resistor with 1.2k resistor & 50uf will give that first gain stage quite a bit of gain.  I'm not sure that would be a Chet Atkins tone?   I love Chet's music  and listen to his stuff quite often.

With respect, Tubenit

[HotBluePlates]

So I understand that there are possibly no 2 Standel 25L15's that are identical; I am going with my take as an experimental 25L15 with many tone options, bias select, etc. Then it will be possible to be very versetile to to emulate say, Grady Martin or Chet. Even Grady sounds different on every session so even if I am getting close it is possibly good enough.

It's probably true that possibly no two are alike. But the amp is also very transparent; every guitar you plug in sounds different, and like that guitar. Therefore, I'd recommend sticking close to the original preamp schematic, as least as a starting point. Then if you plan to modify, leave some extra places for new components to be mounted.

Here is my modified Bob Crooks schematic, with additional adjustments on the first preamp section, and a full Baxandall tone control on the second. I am going to use 6L6's for now, as there are no 807 available in Western Canada
Please feel free to comment and suggestions, before I start drilling holes.

6L6's will work fine. 807's are available from ebay or various tube dealers that sell things other than new production tubes. Antique Electronic Supply sells old stock 807's at $20.80/ea, as well as new Chinese for $15/ea. I bought 14 RCA and G.E. 807's off ebay for less than $10/ea.

Other comments:
-  Looking at my notes, I have ~412v on the 807 plates and 318v on the screens. That rules out ultralinear operation because the screen voltage is very different than the plate voltage. If you try UL connection without making a major bias change (as I tried when I overlooked this originally), plate current will soar and you risk melting your output tubes. Regardless, the 25L15 wasn't ultralinear.

-  Since it was operated in pentode mode, and used cathode biasing, the idle current is fairly high. I regularly idle my 25L15 at ~60mA. The cathode voltage for my amp is generally around 26.5v, so idle dissipation is 412v-26.5v = 385.5v * 0.06A = ~23w.

-  Since the amp is operating class A, there is not much of anything to be gained by fixed/cathode bias switching. There will basically be no sonic difference. You might get an extra watt of output because the 26.5v across the cathode resistor is no usable by the plate, but that's not enough to hear a difference.
   -   I've posted a snippet of the 25L15 output stage I found somewhere on the internet, which appears to match the original output tube circuit. The 100Ω pot shown balances the current in the 2 output tubes; I added a 100Ω pot between the 68Ω resistor and the tube cathodes (the pot is shared by both tubes like the 68Ω) to offer a current adjustment in addition to the current balance original present.

-  Your C23 is useful, and I have a Cut control in its place in my amp. However, the value is way too small to do anything. I personally used a cap from plate and cathode of the phase inverter to either end of a pot wired as a rheostat. Both caps are needed because you have 2 different d.c. voltages to block. With that, the cap values are surprisingly large, because 1) the output impedance of the inverter is so very low compared to 12AX7 inverters; and 2) with the Cut control set for maximum treble cut, the blocking caps are in series and are effectively a single cap of half their individual values. I used a 1MΩ pot and I think I settled on 0.047uF blocking caps. I started with something like 0.01uF each and kept altering the cap value after listening tests because the control wasn't effective with the smaller caps.
   -  You'll probably want a Cut control for single coil guitars like Strats or Teles because the D130 has treble that extends very much higher than normal guitar speakers. I promise you your guitar's tone control will become useful, perhaps for the first time for you.

-  I don't think the Master volume will be any use for you. I haven't had a chance to crank this amp wide open, but the entire architecture is loud and clean. The whole reason to use 12AX7 -> 12AT7 -> 12AU7 is that each successive stage has less gain and accepts larger input signals, so the guitar signal stays clean throughout. If you recall that Chet got his Standel from pedal steel player Jimmy Day, you'll get the idea.

[HotBluePlates]

-  I'd highly recommend sticking to the original Standel tone control circuit, at least for a first build. Your Baxandall circuit doesn't match what Peter Baxandall originally published (he assumed the circuit was between a previous gain stage's plate output and the control grid of a pentode, with a further connection from the pentode's plate back to the Bass control), and doesn't have the center-tapped Treble pot Baxandall used in his published circuit. It would also be advisable to breadboard his circuit while altering the 100pF cap's value to get the Treble to act where you want it.
   -   The other problem is the Standel used triodes to create the feedback loop and to inject the fed-back signal, and I'm unsure how that would interact with Baxandall's circuit. Breadboarding would tell the tale.

-  I would label your P4 as "Mids" and use a 1MΩ wired as a variable resistor, with R6 being the original 30k in the 25L15. If you set that Mid control in my amp to 0, it gives the stock 25L15 midrange dip, and if you increase it to full, it gives a flat response (which sounds in comparison like a mid-boost). With this setup, P8 is not needed.

-  You could vary the caps in the T-filter as you have shown to shift the frequency of the mid-dip, but that's a brute-force way to do it and you only have have 3 settings. I chose to go the other route and use a dual-1MΩ pot to take the place of R4/R5, which allows a smooth sweep to any point between 2 extremes. I used a resistor per section of the dual-pot to set a minimum resistance value of about 50kΩ and a resistor in parallel with each section of the dual-pot to set a maximum resistance of about 500kΩ. That allows the caps to stay constant while the mid-dip is swept.

-  I think you wanted The input stages to be switchable between T-filter and no-T-filter. If so, I'd delete R36 and keep the rest of what you have. That applies the input signal to both halves of the 12AX7, with outputs selected by your SW5 (and a cool idea... I may steal it to try at some point!).
   -   Historical note: the first 25L15's didn't have a second "channel". The 2nd input was requested by Joe Maphis, who wanted to be able to let guests sit in and play through his amp. However, the input jack and volume control for that channel was hidden on the underside of the preamp chassis, so uninvited guests wouldn't know where to plug in to his amp! That "Hide-a-Jack" channel is pretty neutered compared to the main channel, with reduced volume and shaved bass. Apparently, Joe didn't want any guest who did use his amp to outshine him while they were both playing.

Again, if you didn't go back to the thread I linked before and get in contact with "ParkelCEO" I'd strongly encourage you to do so. He's a nice guy and willing to share the details of the original 25L15 (including a lot of things that will make your build easier), and has helped a number of folks, including me, complete this build. He's only concerned that mass publication of the info will negatively impact him or the individual who allowed him to document an original 25L15.

[HotBluePlates]

Almost forgot:
-  I wouldn't use R23 as you have it, prior to the filter caps. It's just wasting heat, and wasn't present in the original 25L15.

-  I think you have your chokes backwards, as the lower-inductance unit will generally go upstream (closer to the rectifier). That's because high-current chokes tend to be wound with fewer turns of fatter wire, and therefore have lower inductance. Lower-current chokes are more readily available in high-inductance values.

-  I used that bigger, lower-inductance choke between the caps you have marked as C32 and C19, with a resistor to drop voltage between C19 and the cap feeding the output tube screens.

[kingplank]

Big thanks to HBP to your tremendous input.

It will take me a while to digest all these notes, seems like its time to go back to the drawing board.

One thing I did not mentioned; is that I am planning to reuse Dynaco ST70 transformers from a previous project, a low power Twin. With the UL mode and fixed bias the voltages were spot on.  I prefer the tone when it is on pentode mode and cathode bias. But with 430v on the plates the amp got real hot real quick so I quit using cathode mode. The UL mode sounded Ok.

The Twin(in stock mode)  sounded very close to the reissue 57 Twin, but my son did not like the tone, so he is still  using his Blues Junior. I played him some old tracks with Standel and he likes the tone very much so that brings us to the Standel project.
I will revise the schematic and repost

[HotBluePlates]

I see what you mean about the reused transformers.

I used a 60w Hammond OT, a big 8lbs. transformer. It was selected because it had the same-sized core as the Standel original.

[kagliostro]

Sorry to give disturbance here

I'm not able to follow the signal in the schematic Kingplank posted 

http://www.el34world.com/Forum/index.php?action=dlattach;topic=14263.0;attach=36291

I see the signal start from V3 go to V5 therefore towards the TS and V4, but I'm not able to see 

where it exits the signal present in V4 to go to the further stage 

could be this night I did not sleep enough

K

[sluckey]

Here's what I see... There are two reference designators for the tubes involved. Since you used the V3, V4, and V5 designators, I will also.

The main signal path is from V3-1 (plate) to V5-2 (grid). V5-1 (plate) is the main signal output to the master control. But V5-1 also sends a signal back to the active tonestack (BAX?). This signal loops around to V5-2. So, the tonestack is controlling the local NFB for V5A.

But there is another loop. The tonestack also connects to V4-7 (grid). The signal on V4 grid couples to V4-8 (cathode) and since V4-8 and V3-3 share a common cathode resistor, this signal is injected back into the main signal path in V3.

That's the signal path thru and around the tonestack. I've never seen this before and don't totally understand it. You may be able to get some theory of operation from the net, or maybe one of our strong theory guys can explain the operation, benefits, etc. 

[HotBluePlates]

But there is another loop. The tonestack also connects to V4-7 (grid). The signal on V4 grid couples to V4-8 (cathode) and since V4-8 and V3-3 share a common cathode resistor, this signal is injected back into the main signal path in V3.

I recommend looking at it as 1 feedback loop. The confusion is that a Baxandall with an extra resistor and without a center-tapped Treble pot are confusing matters.

I'm going to describe stages entirely differently. I'll simply say "12AX7" or "1st 12AT7 stage," etc.

From the 12AX7 input stage, the signal goes to the first 12AT7 stage and gets amplified. It then goes to the 1st 12AU7 stage, which has 2 outputs: C7 and C8. C7 heads back to the tone circuit.

The output of the tone circuit feeds the 2nd 12AT7 stage, which is cathode-coupled to the 1st 12AT7 stage. There is no actual signal output, but due to the inversion of the 1st 12AU7 stage, the 2nd 12AT7 stage is a feedback input. So the tone controls sit inside a feedback loop.

This feedback loop changes how the signal is shaped that appears at the 1st 12AU7 stage, and therefore what gets passed to the 2nd 12AU7 stage, the phase inverter.

If you look at other amplifiers with a feedback loop which returns to a preamp tube cathode, they generally source the feedback from some low-impedance point, like an OT secondary tap. The 25L15 is taking its feedback signal from a high-impedance point (the 1st 12AU7 plate), and therefore needs to have a high impedance triode grid as the place where the feedback is injected. The common cathode arrangement of the 12AT7 allows interface of a high-impedance feedback signal to a low-impedance injection point.

Another subtle point I noticed from measuring voltages at all tube pins in this amp is that the 2nd 12AT7 stage's plate current is very much larger than the plate current of the first 12AT7 stage. That makes sense because there's not a plate load resistor in the way knocking the current down. The big current for that feedback injection point makes it effective at controlling the current of the 1st 12AT7 stage.

Again, subtleties like this is why I strongly recommend talking to the guy with the complete original 25L15 info and copying it directly first, or at least breadboarding both versions. Bob Crooks was a savvy designer, and we'd be hard-pressed to come up with something that does the same but better.

My additions in my version of the 25L15 didn't alter what was originally there, but added flexibility in some areas without sacrificing the ability to set the controls for dead-stock operation. When I did try to get clever and incorporate a Triode/Ultralinear/Pentode switch of the output tubes, I found out quick I didn't think it through enough. I failed to notice the screen voltage is well below plate voltage, which prevents running Triode or Ultralinear mode without excessive plate dissipation (I probably could have monkeyed the bias when the output tubes were set for those modes, but it was my goal to stay close to the original amp's operation).

[kagliostro]

Thanks HotBluePlates (and thanks also to you Steve)

always I've difficulties when there are feedback circuits

(I think that feedback is one of the more difficulties matters on tube amp)

more this circuit with this arrangement is really labyrinthine to my eyes

now I've understand that the effect of the signal fitting the grid of the second 12at7 (V4) affects, through, the cathode the signal present on the first 12at7 (V3)

K

[kingplank]

Thanks guys for all your input.

No luck contacting Parkel so now I have to stick to the "napkin" 25L15 schematic and work with it. Hopefully it is close to the Parkel.

- input T-filter: I understand this is a large part in getting the Standel sound. I've been suggested in experimenting with the values; so instead of soldering and unsoldering parts I use rotay switches which are cheap and I have a lot of holes in my chassis already. I like to use HBP's dual gang pots but  I dont quite understand the resistors setup. So is this a strong mid boost? The Standels sure sound like a lot of mids between the 2nd and open high E.

- I am now scared trying to use Baxandall in the second preamp section, so I am now reverting back to the napkin schematic. I would rather wire up everything and the amp works , and than experiment later.(leaving enough room for extra parts)

- power amp & power supply. After modeling with Duncan amp psu for most of the day,I am not able to bring down my B+ below 400V . I tried Weber's B+ Zener before but they fried easily.
I ran the previous amp with cathode bias at 460V. It sounded better than fixed bias but ran really hot. The only amps that run 6L6's high volts in cathode mode is the Fender Prosonic and some old Eicos. I have no idea the B+ with 807's in the Standel. So that is why the 300 ohm R23 for starters. Permanent solution is a lower voltage transformer; but I want to test this circuit out first before I invest furthur.

Yes, I made an error with placing the chokes. Interesting thing on the Standel power supply schematic: the preamp supplies bypasses the second 10H choke.
The A470 OT weighs 7 pounds, similar to HBP's 8 pounder.

[kingplank]

Napkin schematic, in case you dont have it

[kagliostro]

Kingplank

seems you have an undesired connection dot near to the write V3A Plate

Am I wrong ?

K

[kingplank]

I've been scratching my head over that connection for a long time( between 270K & .047u ?)
I am assuming the feedback tone control is out of phase with output of V2A therefore suppresses the frequencies alterted. The only other circuit that I found has the same idea is this one.
It would  be safer not a connection.

[kagliostro]

Here the junction dot I mean is missing

K

[HotBluePlates]

No luck contacting Parkel so now I have to stick to the "napkin" 25L15 schematic and work with it. Hopefully it is close to the Parkel.

PM sent with more direct contact info. The "napkin schematic" must be from ex-employees of the modern Standel, and has a couple of errors, at least one omission and some modern changes to the circuit.

- input T-filter: I understand this is a large part in getting the Standel sound. ... So is this a strong mid boost?

No, the T-filter is a deep mid-dip. The standard Fender blackface tonestack is a modified and re-arranged T-filter, with a control added to impact midrange.

What is labeled "Contour" on the napkin schematic is similar to what I call my Mid control. Increasing resistance to ground reduces the mid-dip, which sounds like a mid-boost in comparison to the stock sound.

I've been suggested in experimenting with the values; so instead of soldering and unsoldering parts I use rotay switches which are cheap and I have a lot of holes in my chassis already. I like to use HBP's dual gang pots but  I dont quite understand the resistors setup.

Maybe I'll write a post about T-filter in general, and show how to sweep the center-frequency of the mid-dip. Then it's not Standel-specific.

I advocate using the dual-ganged pot because with that setup, I could duplicate every sound available to your rotary switch plus dial the mid-dip to points in-between and beyond your fixed settings.

Also, you may find Contour settings that are useful for a particular guitar/sonic effect/recording track, but are odd enough you don't want to be married to them. So I think the cap-swap approach will require a lot of experimentation beforehand to find what you like. I took what I feel is the easy way out. 

- power amp & power supply. After modeling with Duncan amp psu for most of the day,I am not able to bring down my B+ below 400V .

You're using a replacement ST70 PT from Triode Electronics? If so, the high voltage winding is a little too-high in voltage. It also has much more current capacity on all windings than you'll need, so you can forget about the voltage sagging downward. If anything, it will be even higher.

I still haven't figured out Duncan PSU Designer, but any sim software can lie to you if you don't get all the little details just right.

I have no idea the B+ with 807's in the Standel.

I landed on about 412vdc on the 807 plates, but as high as 430v would also be typical.

Interesting thing on the Standel power supply schematic: the preamp supplies bypasses the second 10H choke.

I'm not sure what you mean. The 120kΩ resistor? I didn't use a resistor like that, nor do I think it is needed. If anything, that resistor is just a bleeder, to ensure B+ voltage drops when you turn the amp off. My 25L15 does that anyway just from the tubes' continued conduction as the heaters cool after the power is switched off.

[PRR]

> I'm not able to follow the signal in the schematic Kingplank posted

Neither am I.

I believe it has more than one error.

[kingplank]

Revisions to my experimental 25L15 schematic

- revised T filter, I hope this is what HBP is talking about

- revised power supply to the Standel schematic, but still retaining R23 300ohm volt dropper

- revised bass control to the "1953 Bob Crooks" schematic

- there is definitely a connection before C7 to V4 plate

[HotBluePlates]

- revised T filter, I hope this is what HBP is talking about

Way too complicated.

With variable resistance, you use only the 2 caps present in the original T-filter.

Look back at the original T-filter in the Bob Crooks schematic. See the pair of 220kΩ resistors? Pretend each resistor is 500kΩ instead; that's one extreme setting of my Contour control. Now pretend the 220kΩ resistors are 50kΩ instead; that's the other extreme setting of the control.

I use 1 section of a dual 1MΩ and 2 more resistors to take the place of each 220kΩ resistor. If you know ohm's law, it's pretty easy to work out how to parallel a resistor across the pot and have a 2nd resistor to sweep between those 2 resistance limits.

- revised power supply to the Standel schematic, but still retaining R23 300ohm volt dropper

L1 is in the wrong place, power amp section is missing a resistor, preamp supply does not match the Bob Crooks schematic posted earlier in this thread.

- there is definitely a connection before C7 to V4 plate

No, there definitely is not. If there was, you amp is a 25w oscillator.

At this point, I'm gonna have to stop making corrections as I'm already way to close to describing the circuit detail-by-detail. That runs counter to the agreement I made when receiving the info for my build. I'm afraid a sharp builder already has almost every detail they could possibly need to replicate this.

[kingplank]

Thanks for all your help and support; it has been much more than I expected. There is no turning back.

[tubenit]

OK, I was privileged to hear HotBluePlates  25L15 type amp in person.

HBP tends to be somewhat reserved, not prone to exaggerate and understates things at times (perhaps?).

This is a REALLY great amp!

Simply put, it is the warmest richest clearest most articulate clean amp tone that I've ever heard !!!!!   Never heard any Fender that I think could match what I heard today.  It was that good.  No reverb no effects and it had a remarkably rich full resonant tone to it. Amazing!

HBP's  Gretch guitar is definitely a factor in getting the Chet tone.  He's always been a good player and he's doing a decent job of getting that Chet and Jerry Reed sound now.

Fun hearing him play and hearing a GREAT sounding amp!  

with respect, Tubenit

[plexi50]

This is really a great mystery thread. I have been interested in building this amp since last year. Sounds like a great amp with that big fat 15" speaker. Never hear 807 power tubes before. Sooner or later i will make an attempt

[HotBluePlates]

Never hear 807 power tubes before.

They're 6L6GB's (25w) in a different bottle. Regular 6L6GC's should do the same.

... it is the warmest richest clearest most articulate clean amp tone that I've ever heard !!!!!   Never heard any Fender that I think could match what I heard today.  It was that good.

Maybe a Showman with the 2x15 cab with JBL's could do similar.

It's a pretty good-sounding amp. It almost gets some hair on the notes at full volume. Thanks to Tubenit, no one's saying "Now that's an awesome-sounding ugly amp!"