Planning HRM build, advice needed on caps and resistors

[thejaf]

Hello all, this is my first new topic post. I'm gearing up to build an HRM clone and would like some advice. I've gotten most of my answers searching the forum, but I have some specific questions regarding caps and resistors.

First, I have a decent supply of those little yellow polyprop caps (IC, 630V) from previous modding and builds. Are these OK, or should I splurge and buy the 716 orange drops? Will I notice any tone difference between these two types of caps?

Second, I picked up a LOT of resistors that came from a Pennsylvania wireless company that went out of business about eight years ago. I've used them to date for all my tube amp projects with great results, and mostly was wondering if anyone can ID them for me. They are all 1/2watt size, and the bodies are a dark, very shiney maroon color with a gold tolerance band. Anytime I've measured them before inserting into a circuit, they've been right on the value, less then 1% variance. I was told they are ceramic, but would like some opinions on these. I've read here that it's very important to avoid carbon comp on the plates of these clones, and was wondering if these mystery resistors work on the plates of my HRM build if they are indeed ceramic.

Thanks!
Jeff

[dogears]

Why 716? Dumble never used them.....

I'd stick with the Dales on the plates for my 2c

I hope you paid careful attention to the errors in the existing schematics when you searched the forum....

Hello all, this is my first new topic post. I'm gearing up to build an HRM clone and would like some advice. I've gotten most of my answers searching the forum, but I have some specific questions regarding caps and resistors.

First, I have a decent supply of those little yellow polyprop caps (IC, 630V) from previous modding and builds. Are these OK, or should I splurge and buy the 716 orange drops? Will I notice any tone difference between these two types of caps?

Second, I picked up a LOT of resistors that came from a Pennsylvania wireless company that went out of business about eight years ago. I've used them to date for all my tube amp projects with great results, and mostly was wondering if anyone can ID them for me. They are all 1/2watt size, and the bodies are a dark, very shiney maroon color with a gold tolerance band. Anytime I've measured them before inserting into a circuit, they've been right on the value, less then 1% variance. I was told they are ceramic, but would like some opinions on these. I've read here that it's very important to avoid carbon comp on the plates of these clones, and was wondering if these mystery resistors work on the plates of my HRM build if they are indeed ceramic.

Thanks!
Jeff

[Bob-I]

First, I have a decent supply of those little yellow polyprop caps (IC, 630V) from previous modding and builds. Are these OK, or should I splurge and buy the 716 orange drops? Will I notice any tone difference between these two types of caps?

You'll notice a tone difference with every type of cap but IME the orange drop PS series of the xicon Metalized polyprop are the best. I've also used the xicon metalized polyester and they sound good too, about the same as the 715 orange drops. The 716 are not the ideal, if you're gonna buy caps, get the xicon MPP IMO.

Second, I picked up a LOT of resistors that came from a Pennsylvania wireless company that went out of business about eight years ago. I've used them to date for all my tube amp projects with great results, and mostly was wondering if anyone can ID them for me. They are all 1/2watt size, and the bodies are a dark, very shiney maroon color with a gold tolerance band. Anytime I've measured them before inserting into a circuit, they've been right on the value, less then 1% variance. I was told they are ceramic, but would like some opinions on these. I've read here that it's very important to avoid carbon comp on the plates of these clones, and was wondering if these mystery resistors work on the plates of my HRM build if they are indeed ceramic.

These might be fine for the series resistors and cathodes, but for the plates stick to the vishay dale metal film, mouser part # 71-RN65D-<value>. There's no question in my ears that these make a huge difference in the brightness of the amp. My amp was dull and lifeless until dogears suggested these, now it's bright and alive!!

Also, use the cheepy ceramic disk caps on all the pF range caps, buy extras and check them for DC leakage and value. These add a grainyness to the tone that cannot be had with any other caps.

[thejaf]

Thanks for the reply! I'll buy some Dales for the plates with my Mouser order. I'm planning to use Bob-I's recent HRM schematic with your recommendations and pointers (previous post). I've been reading the posts for a couple months, saved a buch, and I'm finally getting ready to start the build myself.

Couple other things:

1. I've order a JTM45 OT from Weber, going to use the 6600 primary to run a pair of KT66s.

2. I'm planning to order the Hammond 272JX power tranny (300-0-300) from Antique. This should provide 400 to 420B+ on the KT66 plates, and then drop to the recommended voltages on the preamp plates (200, etc).

3. Going with Sprague Atom filter caps (100uf in series first stage, the 3 stages of 22uf thereafter).

4. I plan to put the HRM controls and OD trim on the front panel, given my obsession for constant tweeking.

[Bob-I]

1. I've order a JTM45 OT from Weber, going to use the 6600 primary to run a pair of KT66s.

I used a similar OT from AES for one build using EL-34's. It sounds great. I also used one of these exact OT's for a JTM-45 with KT66's and it too sounds great.

2. I'm planning to order the Hammond 272JX power tranny (300-0-300) from Antique. This should provide 400 to 420B+ on the KT66 plates, and then drop to the recommended voltages on the preamp plates (200, etc).

I used this one in a 6V6 version I built a long time ago. I only had to adjust one resistor on the PS rail to get the voltages in line.

4. I plan to put the HRM controls and OD trim on the front panel, given my obsession for constant tweeking.

I'm thinking of something similar. Maybe switching the PAB along with the OD and using the HRM controls for adjustment of the OD side.


Has anyone realized that we have our own language here, PAB, HRM, CL1, OD2 3 acronyms in a sentence is scary

[thejaf]

Great, looks like I'm on the right track then! The "clone" I built about three or four years ago used that same Hammond PT with an OEI 50-watt Plexi OT running a pair of Groove Tubes EL34S. I took the finished product to a HCAF AmpFest in northern Virginia, and it was well liked, but not quite as smooth sounding as the soundclips I've heard on this website so far. The clean was Fenderish with a bit more midrange and the dirty was close in tone to the Rythm channel of a Mesa Mark III with a tad more gain. The schematic I used at the time was one floating on a popular website before it was "removed due to threatening communication" or some similar BS. Following the schematic directly at that time resulted in a very unstable amp; I even built it twice to make sure I didn't miss anything, with the same results. Therefore, I followed the Soldano SLO/Marshall JCM theory of raising the cathode resistor of the last gain stage to 10K, which solved the stability problems. I'm really excited about this build, mostly the feedback and support of a forum dedicated to this amp design.

Has anyone realized that we have our own language here, PAB, HRM, CL1, OD2 3 acronyms in a sentence is scary

I'm used to it, as I write technical reports and letters to state agencies. Acronyms gallore

[swt]

just for the sake...make sure that all plates resistors are metal film...or your tone is gone. if you wanna go with carbon, etc, in other places, it's up to you, but plate resistors are a must.
What schem are you refering to?. can you send it to me?
swtnqn@yahoo.com.ar.
dogears is THE man when it comes to HRM. follow his instructions for an unbelievable tone!!

[oldmacman]

How close are the polyprop capacitors that Ted Weber sells to the Xicon MPP's?

[Easy]

Has anyone realized that we have our own language here, PAB, HRM, CL1, OD2 3 acronyms in a sentence is scary

Yah. Newbie, here. It keeps me searching, I'll tell you!

But, please continue. This is very helpful.

[Easy]

oldmacman: Never did an A/B compare, but the Weber caps sound good to me. I don't use them much because they're so HUGE compared to the Xicon.

[Bob-I]

How close are the polyprop capacitors that Ted Weber sells to the Xicon MPP's?

They're not bad, but I've had several bad one's in his kits, plus they're easy to kill with a little too much heat. Get the xicon's if you don't allready have the webers.

[ODwan]

Has anyone realized that we have our own language here, PAB, HRM, CL1, OD2 3 acronyms in a sentence is scary

Yah. Newbie, here. It keeps me searching, I'll tell you!

But, please continue. This is very helpful.

A short rundown:
PAB : PreAmpBoost (diconnects some portion of the tonestack)
HRM : HotRubberMonkey (fancy name for a tonestack after OD2)
CL1, CL2 : tube stage naming of the first and second stage of the Clean channel aka V1a and V1b
OD1, OD2 : tube stage naming of the first and second stage of the Overdrive channel aka V2a and V2b
R/J : Rock/Jazz switch of the tonestack

Timo

[Easy]

A short rundown:
PAB : PreAmpBoost (diconnects some portion of the tonestack)
HRM : HotRubberMonkey (fancy name for a tonestack after OD2)
CL1, CL2 : tube stage naming of the first and second stage of the Clean channel aka V1a and V1b
OD1, OD2 : tube stage naming of the first and second stage of the Overdrive channel aka V2a and V2b
R/J : Rock/Jazz switch of the tonestack

Timo

Thanks so much, ODwan. This is a great help!


_

[Luthierwnc]

More jargon:

ODs: Sprague Orange Drop capacitors. There are several types
MF: Metal Film (comments limited to resistors)
CF: carbon film resistors modern resistors used for vintage style amps
CC: carbon composition (traditional 1960's resistors)
RN65: military spec metal film resistors that work well with these amps
Atom: Sprague filter caps (look like M80 firecrackers)
MMP: Xicon polypropylene coupling caps popular with D amp makers
MM: Mercury Magnetics custom transformers

Search speakers here and on the GearPage for speaker terms

Hope this helps, Skip

[Easy]

Thanks, Skip. Knew most of these, but not MMP or RN65.